[Ci] Refactor CI workflows into modular suites

[veblush]

Changes:

• Modular Suites: Consolidated tests into reusable suite_*.yml workflows (Core, Cortex-M, Xtensa, etc.).
• Scoping: Standardized basic, extended, and all scopes for platform tests.
• Optimized Triggers:
  • pr_ready.yml runs standard checks.
  • pr_full.yml runs only extended checks (avoiding duplicates).
  • merge_group.yml runs the full suite reliably.
• Cleanup: Renamed files for consistency (run_, test_) and removed obsolete workflows.

BUG=n/a