Add support for PEP 751 pylock.toml lockfiles

[Adityatorgal17]

Fixes #4638

What this PR does

Adds support for parsing PEP 751 pylock.toml lockfiles, including:

• Dependency extraction
• Virtual environment package modeling
• Comprehensive test coverage

Tests

• Added tests/packagedcode/test_pylock.py
• Added test fixtures under tests/packagedcode/data/pylock
• All tests/packagedcode tests pass

Notes

• Follows existing DatafileHandler patterns
• Gracefully handles malformed or incomplete lockfiles

[Adityatorgal17]

Hi @AyanSinhaMahapatra 👋
This PR is ready for review.
Some CI jobs are waiting for approval since this is from a fork.
Whenever you have time, could you please take a look?

Thanks!