Update GitHub Actions versions and gitignores

[SoundGoof]

Summary

Update outdated GitHub Actions dependencies

Changes

• Update actions/upload-artifact from v4 to v7.
• Update actions/cache from v4 to v6.
• Ignore local VS Code settings.
• Ignore generated native-extension and C coverage artifacts.

Testing

• Validated all workflows with actionlint.
• Validated workflow YAML with yamllint.
• Ran 44 system tests successfully.
• Ran all 44 system tests under Valgrind with no errors or lost memory.
• Ran all 44 system tests under ASan and UBSan with no sanitizer errors.
• Generated the C coverage report successfully with 59.93% line coverage.