build: ➖ Remove pkg_resources usage to fix Python 3.12 failure

[pekat-vojtech-kovacik]

Motivation

Python 3.12 removes pkg_resources, which causes MMCV to fail during PEP 517
build isolation with the following error:

ModuleNotFoundError: No module named 'pkg_resources'

This breaks installation for Python 3.12, even though the affected code paths are only used for version handling.

Modification

Replaces: pkg_resources.get_distribution and pkg_resources.parse_version
with: importlib.metadata.version and packaging.version.parse

Removes pkg_resources from build/tooling configuration

Use cases (Optional)

This change allows MMCV to be installed successfully on Python 3.12

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects, like MMDet or MMCls.
• CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.