Run Ruff only on selected changed Python files in PRs (#71) - #110

This PR addresses Issue #71 by optimizing the Ruff linting process in the CI pipeline.

What’s implemented:

• Introduced a custom Ruff workflow that:
  • Detects changed .py files only in the api-server/ and state-manager/ directories.
  • Runs ruff check only on those changed files during PRs and pushes.
  • Skips Ruff if no relevant Python files were modified.
• No longer uses the predefined astral-sh/ruff-action, which scanned the entire folders.
• Instead, Ruff is installed manually and executed selectively on modified files — making the workflow more efficient and faster.