Address Issues 99-100: Remove CodeQL and refactor Treesitter

[rahlk]

Motivation and Context

This PR removes CodeQL as an analysis backend and makes Tree-sitter the default backend. CodeQL was previously included but is no longer available in this repo.

How Has This Been Tested?

The following tests were performed:

• Verified that all existing functionality works correctly with Tree-sitter as the default backend.
• Updated and re-ran the test suite, achieving 77% coverage.
• All 120/120 tests pass successfully.
• Manually tested common usage scenarios to ensure expected behavior.
• Validated that no residual CodeQL dependencies remain in the codebase.

Breaking Changes

• CodeQL support is fully removed: Users who previously relied on CodeQL must now transition to Tree-sitter.
• Tree-sitter is no longer optional: It is now the default and only supported backend.
• No changes required for users already using Tree-sitter.

Types of Changes

• Breaking change (fix or feature that would cause existing functionality to change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the Codellm-Devkit Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional Context

• Improved internal documentation to reflect the removal of CodeQL.
• Updated test cases to validate Tree-sitter as the primary backend.
• Streamlined backend selection logic to remove unnecessary checks for CodeQL.

New Badges for Test Status