SG-37222 new way to handle python third parties

[eduardoChaucaGallegos]

This pull request introduces a major overhaul to the way third-party Python dependencies are managed and loaded in the project, focusing on the tank_vendor mechanism. The changes centralize dependency management using versioned pkgs.zip files, implement a robust dynamic import hook for the tank_vendor namespace, and improve documentation and maintainability. Legacy or redundant scripts and files are removed, and package-specific patches are handled more cleanly.

Dependency Management and Loading Redesign:

• Introduced a new dynamic loading mechanism in tank_vendor/__init__.py that auto-discovers and loads third-party packages from version-specific pkgs.zip files, supports lazy aliasing for the tank_vendor.* namespace, and applies package-specific patches (e.g., for shotgun_api3 SSL certificates). This includes a custom meta path finder and robust error handling for missing or invalid ZIP files.
• Updated the documentation in developer/README.md to describe the new requirements folder structure, the workflow for updating bundled dependencies, and the rationale behind using pkgs.zip files for consistent and reproducible environments. [1] [2]

Import and Compatibility Improvements:

• Enhanced the import handler in python/tank/bootstrap/import_handler.py to correctly skip SourceFileLoader for modules inside ZIP files, ensuring compatibility with the new packaging approach.
• Removed the legacy upgrade_pyyaml.py script, as dependency upgrades are now handled via the new requirements workflow and automation.

Cleanup and Maintenance:

• Removed redundant or now-unmanaged files from vendored packages, such as packaging/__init__.py and packaging/_structures.py, as these are now managed within the ZIP-based dependency system. [1] [2]
• Updated copyright years and added detailed module-level docstrings.

These changes modernize and streamline dependency management for the project, making it more maintainable and robust across Python versions and environments.

Resolves #914

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.42%. Comparing base (187b794) to head (a9a1aa3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #996   +/-   ##
=======================================
  Coverage   79.42%   79.42%           
=======================================
  Files         198      198           
  Lines       20749    20751    +2     
=======================================
+ Hits        16479    16481    +2     
  Misses       4270     4270           

Flag	Coverage Δ
Linux	78.89% <100.00%> (+<0.01%)	⬆️
Python-3.10	79.24% <100.00%> (+<0.01%)	⬆️
Python-3.11	79.00% <100.00%> (-0.14%)	⬇️
Python-3.13	79.14% <100.00%> (+<0.01%)	⬆️
Python-3.9	79.21% <100.00%> (+<0.01%)	⬆️
Windows	78.92% <100.00%> (+<0.01%)	⬆️
macOS	78.90% <100.00%> (+<0.01%)	⬆️

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[carlos-villavicencio-adsk]

LGTM. The init.py file it's too big in my opinion. It would be great to have a better organization/modularization there. Maybe we can consider using a main.py file? These are just thoughts.

Besides this, I think we should start testing this throughoutly.

[julien-lang]

A few changes please. Also, I agree with all comments from Charlie so could you address them please?

And could you add some unit tests validating the import and handle of third partiy libs