fix issues in discovering ruff in pip build environments

[jsurany]

Summary

Changes in this PR #13591 did not allow correct discovery in pip build environments.

# both of these variables are tuple[str, str] (length is 2)
first, second = os.path.split(paths[0]), os.path.split(paths[1])

# so these length checks are guaranteed to fail even for build environment folders
if (
    len(first) >= 3
    and len(second) >= 3 
    ...
)

Here we instead use pathlib, and we check all pip-build-env- paths for the folder that is expected to contain the ruff executable.

Here we update the logic to more properly split out the path components that we use for pip-build-env- inspection.

Test Plan

I've checked this manually against a workflow that was failing, I'm not sure what to do for real tests. The same issues apply as with the previous PR.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[gaborbernat]

Needs some work IMHO.

[gaborbernat]

👍

[charliermarsh]

What was the actual problem here?

[gaborbernat]

What was the actual problem here?

#13591 does not work 😆 this fixes that. @jsurany is a colleague of mine and when validating that release discovered this issue.