File generation is slow

Hi!

I'm generating `*.validate.rs` files with `buf` with
```yaml
- local: protoc-gen-prost-validate
out: generated/rust/src/grpc
strategy: all
opt:
- enable_type_names
```
and
> buf generate --timeout 0
however this usually takes **5-7 minutes**. I'd rather it took a few seconds tops.

Any ideas where the slowness could be and what could be done about it? I'll gladly help :)

Note:
* I have 503 .proto files
* defining 8428 messages and 1828 enums
* and 5367 validation annotations

Start by profiling the reported `buf generate --timeout 0` command with the provided configuration and the stated 503 `.proto` files, 8,428 messages, and 1,828 enums. Investigate where `protoc-gen-prost-validate` spends its time during generation, then confirm that the identified bottleneck is addressed by rerunning the command and comparing its duration with the reported 5–7 minutes.

Written by the indexing model from the issue text.