Multistage builds do not get cached

**Describe the bug**
If you have a Dockerfile with multiple steps that is being used by multiple services like this:

Repository: https://gitlab.com/chocolateimage/multistage

compose.yaml

```
services:
service1:
build:
target: service1
dockerfile: Dockerfile

service2:
build:
target: service2
dockerfile: Dockerfile

service3:
build:
target: service3
dockerfile: Dockerfile

service4:
build:
target: service4
dockerfile: Dockerfile
```

And the Dockerfile:

```Dockerfile
FROM alpine:latest AS base
WORKDIR /app

FROM base AS deps
COPY dependency-generator.sh /app/
RUN [ "./dependency-generator.sh" ]

FROM base AS service-base
COPY service-runner.sh /app

# Pretend all of the services below do different things

FROM service-base AS service1
COPY --from=deps /app/deps /app/deps
ENTRYPOINT [ "./service-runner.sh", "service1" ]

FROM service-base AS service2
COPY --from=deps /app/deps /app/deps
ENTRYPOINT [ "./service-runner.sh", "service2" ]

FROM service-base AS service3
COPY --from=deps /app/deps /app/deps
ENTRYPOINT [ "./service-runner.sh", "service3" ]

FROM service-base AS service4
COPY --from=deps /app/deps /app/deps
ENTRYPOINT [ "./service-runner.sh", "service4" ]
```

The `deps` stage will be executed multiple times, this does not happen with Docker itself. In this example it will not do much, but in a real setting where you would download stuff and do CPU intensive work, this can slow down the build process by a large amount.

**To Reproduce**
Steps to reproduce the behavior:
1. `git clone https://gitlab.com/chocolateimage/multistage.git`
2. `podman-compose build`
3. The line `"Generating" your dependencies` gets printed multiple times

**Expected behavior**
The stage for generating dependencies only gets executed once and cached for the other `COPY --from` commands, just like in Docker.

**Actual behavior**
What is the behavior you actually got and that should not happen.

**Output**

```
$ podman-compose version
podman-compose version 1.5.0
podman version 5.5.2

$ podman version
Client: Podman Engine
Version: 5.5.2
API Version: 5.5.2
Go Version: go1.24.4
Git Commit: e7d8226745ba07a64b7176a7f128e4ef53225a0e
Built: Fri Jun 27 10:15:44 2025
OS/Arch: linux/amd64

$ podman-compose build
[1/7] STEP 1/2: FROM alpine:latest AS base
[1/4] STEP 1/2: FROM alpine:latest AS base
[1/5] STEP 1/2: FROM alpine:latest AS base
[1/6] STEP 1/2: FROM alpine:latest AS base
[1/4] STEP 2/2: WORKDIR /app
[1/5] STEP 2/2: WORKDIR /app
[1/6] STEP 2/2: WORKDIR /app
--> Using cache 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7
--> 95933deb20a3
--> Using cache 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7
[3/4] STEP 1/2: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS service-base
--> 95933deb20a3
[3/5] STEP 1/2: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS service-base
[1/7] STEP 2/2: WORKDIR /app
--> Using cache 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7
--> 95933deb20a3
[3/4] STEP 2/2: COPY service-runner.sh /app
[3/5] STEP 2/2: COPY service-runner.sh /app
[2/6] STEP 1/3: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS deps
[2/6] STEP 2/3: COPY dependency-generator.sh /app/
--> Using cache 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7
--> 95933deb20a3
[2/7] STEP 1/3: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS deps
[2/7] STEP 2/3: COPY dependency-generator.sh /app/
--> Using cache 034fcc266fb6114d2937ab288fa83ea807d0e66a8feb3dc82ad0c98314fd540d
--> 034fcc266fb6
[2/6] STEP 3/3: RUN [ "./dependency-generator.sh" ]
--> Using cache 034fcc266fb6114d2937ab288fa83ea807d0e66a8feb3dc82ad0c98314fd540d
--> 034fcc266fb6
[2/7] STEP 3/3: RUN [ "./dependency-generator.sh" ]
"Generating" your dependencies...
--> a56b1948e08e
[4/4] STEP 1/3: FROM a56b1948e08e85a3b8f4afe5b1f38ae741e65042e3de3bb0ac4f1fd4665232ca AS service1
[4/4] STEP 2/3: COPY --from=deps /app/deps /app/deps
[2/4] STEP 1/3: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS deps
"Generating" your dependencies...
[2/4] STEP 2/3: COPY dependency-generator.sh /app/
--> e0bd0f2bd1b2
[2/5] STEP 1/3: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS deps
[2/5] STEP 2/3: COPY dependency-generator.sh /app/
--> Using cache 034fcc266fb6114d2937ab288fa83ea807d0e66a8feb3dc82ad0c98314fd540d
--> 034fcc266fb6
[2/4] STEP 3/3: RUN [ "./dependency-generator.sh" ]
--> Using cache 034fcc266fb6114d2937ab288fa83ea807d0e66a8feb3dc82ad0c98314fd540d
--> 034fcc266fb6
[2/5] STEP 3/3: RUN [ "./dependency-generator.sh" ]
"Generating" your dependencies...
"Generating" your dependencies...
Done
Done
--> 385e7c36c476
--> dd616ccca2ac
Done
[3/7] STEP 1/2: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS service-base
--> Using cache 385e7c36c476103bb79d835758d030cf0deb5ac2a42783f480b2d27d99c694dd
--> 385e7c36c476
[3/6] STEP 1/2: FROM 95933deb20a39176801eb47bad90d1eebb5a975555ad3cc92231bdc5efec4de7 AS service-base
[3/7] STEP 2/2: COPY service-runner.sh /app
[3/6] STEP 2/2: COPY service-runner.sh /app
Done
--> Using cache 385e7c36c476103bb79d835758d030cf0deb5ac2a42783f480b2d27d99c694dd
--> 385e7c36c476
[5/5] STEP 1/3: FROM e0bd0f2bd1b2f166f2240ada9817708cc89e344e0c06d67c082fc59d82fa3a09 AS service2
[5/5] STEP 2/3: COPY --from=deps /app/deps /app/deps
--> Using cache a56b1948e08e85a3b8f4afe5b1f38ae741e65042e3de3bb0ac4f1fd4665232ca
--> a56b1948e08e
--> Using cache a56b1948e08e85a3b8f4afe5b1f38ae741e65042e3de3bb0ac4f1fd4665232ca
--> a56b1948e08e
[6/6] STEP 1/3: FROM a56b1948e08e85a3b8f4afe5b1f38ae741e65042e3de3bb0ac4f1fd4665232ca AS service3
[7/7] STEP 1/3: FROM a56b1948e08e85a3b8f4afe5b1f38ae741e65042e3de3bb0ac4f1fd4665232ca AS service4
[6/6] STEP 2/3: COPY --from=deps /app/deps /app/deps
[7/7] STEP 2/3: COPY --from=deps /app/deps /app/deps
--> 7ae956fbd264
--> 15ca8285fd4c
--> a9360b9c3962
--> 0245a875c6f2
[5/5] STEP 3/3: ENTRYPOINT [ "./service-runner.sh", "service2" ]
[4/4] STEP 3/3: ENTRYPOINT [ "./service-runner.sh", "service1" ]
[7/7] STEP 3/3: ENTRYPOINT [ "./service-runner.sh", "service4" ]
[6/6] STEP 3/3: ENTRYPOINT [ "./service-runner.sh", "service3" ]
[5/5] COMMIT multistage_service2
[6/6] COMMIT multistage_service3
[4/4] COMMIT multistage_service1
[7/7] COMMIT multistage_service4
--> 7af36609ab82
Successfully tagged localhost/multistage_service4:latest
--> 74767c5e34ff
--> f257e791174d
Successfully tagged localhost/multistage_service3:latest
Successfully tagged localhost/multistage_service2:latest
--> 108129ec59fd
Successfully tagged localhost/multistage_service1:latest
7af36609ab8204af22d5df7bdde61fbf9320a61eec2dbf17df9e3cca16b5e997
74767c5e34ffd950a0da07fbb84e788e722d90fdc389b5403d7c935a5c720ab4
f257e791174d390653459aeafc5502c929e13558c035e7ca7fe2fee37ea028c7
108129ec59fdac8160f06ae07fa8baba7726782d616fd46aa8afd86df3232705

```

**Environment:**
- OS: Linux
- podman version: 5.5.2
- podman compose version: f7eeda1a3db10952424af6a5b0501c269ebe3f0d

**Additional context**

Tested in a fresh libvirt/QEMU machine with Arch Linux. I uploaded the example code on GitLab: https://gitlab.com/chocolateimage/multistage

Start by cloning the linked multistage repository and running podman-compose build to reproduce the repeated dependency generation. Then trace how podman-compose handles multiple build targets and shared multistage stages; done means the deps stage runs once and its result is reused while all four services build successfully.

Written by the indexing model from the issue text.