[Bug]: py_layer_tier ignores `root`

### What happened?

...or I don't understand what it's supposed to do.

Given a `py_layer_tier` like:
```
py_layer_tier(
name = "my_tier",
root = "/my_favorite_dir",
)
```

I expect it to put the files in `/my_favorite_dir/my_app.runfiles`, or perhaps `/my_favorite_dir.runfiles`. I'm not sure.

Instead, it puts the files in `/app.runfiles`.

I'm seeing this on a full image build. To save time, I've done the reproduction with `py_image_layer` + checking the output tars.

### Version

Development (host) and target OS/architectures:
Tested on:
Linux x86-64 host and target
MacOS arm host and target

Output of `bazel --version`: bazel 9.2.0

Version of the Aspect rules, or other relevant rules from your
`WORKSPACE` or `MODULE.bazel` file: 2.0.0-alpha.6

Language(s) and/or frameworks involved: Python

### How to reproduce

```shell
First, set up a repository containing:
MODULE.bazel:

module(
name = "no-root",
version = "0.1.0",
)

bazel_dep(name = "aspect_rules_py", version = "2.0.0-alpha.6")

BUILD.bazel:

load("@aspect_rules_py//py:defs.bzl", "py_binary", "py_image_layer", "py_layer_tier")

py_binary(
name = "main",
srcs = ["main.py"],
deps = [],
)

py_layer_tier(
name = "my_tier",
root = "/my_favorite_dir",
)

py_image_layer(
name = "image",
binary = ":main",
layer_tier = "//:my_tier",
)

main.py:

print("Hello, world!")

Build the image layers:

bazel build //:image

Check the contents of the output tar:

tar -ztf bazel-bin/image_default.tar.gz | head

Expectation:
Something like `/my_favorite_dir/my_app.runfiles/_main/._main.venv/bin/python`

Actual result:
A list of files like:
`./app.runfiles/_main/._main.venv/bin/python`
```

### Any other information?

_No response_

Start with the py_layer_tier and py_image_layer definitions, using the BUILD.bazel reproduction and its root attribute as the entry point. Run bazel build //:image, then inspect bazel-bin/image_default.tar.gz with tar to compare the generated paths with the requested /my_favorite_dir location. Done means root affects the runfiles paths in the output tar.

Written by the indexing model from the issue text.