feat: allow skipping python setup

[SMoraisAnsys]

This pull request adds a skip-python-setup input to the affected composite actions. The default value is false, which leads to keeping the same behavior as before. When set to true:

• The _setup-python step is skipped entirely, leaving $GITHUB_PATH untouched.
• A validation step checks that the Python already on PATH matches the version specified in the python-version input (supports both major.minor and major.minor.micro precision), failing fast with a clear error message if there is a mismatch.

This provides flexibility for container-based environments with a pre-installed Python when the current implementation does not. As a matter of fact, the latest release of ansys/actions can't be used to build wheelhouse in a rocky container due to glibc incompatibilities, even if one does manually install python before calling ansys/actions/build-wheelhouse.

The affected actions are currently limited to build-library, build-wheelhouse, doc-build and tests-pytest as they are the ones most likely benefiting from it. The build ones would allow to build on specific environments, e.g. rocky; the doc and tests ones are used in some of our self-hosted runners.

[SMoraisAnsys]

I tested the build-wheelhouse changes and it:

• worked here (wheelhouse for rocky)
• failed as expected here (wrong python checking)

[RobPasMue]

Big pitfall IMO with this check - I'm fine with the skipping logic but we should definitely remove the check introduced to match the python-version input

[RobPasMue]

LGTM! Thanks @SMoraisAnsys

[MaxJPRey]

Nice. I would be curious to see how much time we can save at large in the ecosystem with this option set to false 😃