Add graph expansion and cross-encoder reranking features

- Implemented GraphExpander to enhance search results with related symbols using precomputed neighbors.
- Added CrossEncoderReranker for second-stage search ranking, allowing for improved result scoring.
- Created migrations to establish necessary database tables for relationships and graph neighbors.
- Developed tests for graph expansion functionality, ensuring related results are populated correctly.
- Enhanced performance benchmarks for cross-encoder reranking latency and graph expansion overhead.
- Updated schema cleanup tests to reflect changes in versioning and deprecated fields.
- Added new test cases for Treesitter parser to validate relationship extraction with alias resolution.

codex-lens/pyproject.toml

@@ -49,6 +49,12 @@ semantic-directml = [
     "onnxruntime-directml>=1.15.0",  # DirectML support
 ]
 
+# Cross-encoder reranking (second-stage, optional)
+# Install with: pip install codexlens[reranker]
+reranker = [
+    "sentence-transformers>=2.2",
+]
+
 # Encoding detection for non-UTF8 files
 encoding = [
     "chardet>=5.0",