[Bug]: venv python shim crashes when current directory contains file or directory named "python" or "python3"

[ctcjab]

What happened?

Reproduction Steps

# In a project using aspect_rules_py 1.6.4, run one of the `.venv` targets that gets generated by a `py_test` target. E.g. using http://github.com/chicagotrading/shorty:

bash-5.2$ bazel run //app:app_test.venv
...
To activate the virtualenv in your shell run
    source /Users/joshua.bronson/clones/oss/shorty/.app+app_test.venv/bin/activate

# Activate the virtualenv as instructed
bash-5.2$ source /Users/joshua.bronson/clones/oss/shorty/.app+app_test.venv/bin/activate

# confirm it worked
bash-5.2$ which python3
/Users/joshua.bronson/clones/oss/shorty/.app+app_test.venv/bin/python3
bash-5.2$ python3 -c 'import pytest' && echo it worked
it worked

# trigger the crash by creating any file or directory named "python3" or "python"
bash-5.2$ touch python3
bash-5.2$ python3 -c 'import pytest' && echo it worked
thread 'main' panicked at py/tools/venv_shim/src/main.rs:200:50:
called `Result::unwrap()` on an `Err` value: RunfilesDirNotFound
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Version

Development (host) and target OS/architectures:

Output of bazel --version: aspect 2025.19.5+06d8a1c78

Version of the Aspect rules, or other relevant rules from your
WORKSPACE or MODULE.bazel file: aspect_rules_py 1.6.4

Language(s) and/or frameworks involved: Python

How to reproduce

Any other information?

No response

[arrdem]

Some ideas from chatting with @ctcjab in slack

• This codepath could use isdir tests; we know that the executable can't also be a directory and this is a common case of possible collisions
• This codepath could also use realpath resolution to decide of current_executable().absolute() is the same as the candidate's absolute path. We just need to be careful to not use the resolved absolute path.

Both are probably solid improvements.