- Add `association_tree` module with components for building and processing call association trees using LSP call hierarchy capabilities.
- Introduce `AssociationTreeBuilder` for constructing call trees from seed locations with depth-first expansion.
- Create data structures: `TreeNode`, `CallTree`, and `UniqueNode` for representing nodes and relationships in the call tree.
- Implement `ResultDeduplicator` to extract unique nodes from call trees and assign relevance scores based on depth, frequency, and kind.
- Add unit tests for `AssociationTreeBuilder` and `ResultDeduplicator` to ensure functionality and correctness.
- Implement comprehensive unit tests for the LspGraphBuilder class to validate its functionality in building code association graphs.
- Tests cover various scenarios including single level graph expansion, max nodes and depth boundaries, concurrent expansion limits, document symbol caching, error handling during node expansion, and edge cases such as empty seed lists and self-referencing nodes.
- Utilize pytest and asyncio for asynchronous testing and mocking of LspBridge methods.
