Cleanup pluggable-libs & fix CI file output (#433, #447)

[PraveenMudalgeri]

Summary

This PR makes two targeted improvements:

1. Remove pluggable-libs Submodule

• Deleted the unused submodule entries.
• Cleaned up references in .gitmodules, documentation, and source code.
• Fully resolves issue Remove deprecated Python versions faif/python-patterns#433.

2. Fix GitHub Actions check_changes Output

• Updated the workflow to convert multiline file lists into a single-line, space-delimited string before writing to $GITHUB_OUTPUT.
• Prevents errors such as:
  • invalid format
  • Unable to process file command 'output'

Impact

These changes ensure a cleaner codebase and more reliable CI checks.