incoming_calls tool to the MCP serve

[netbrah]

This pull request adds a new incoming_calls tool to the MCP server, which enables users to find all callers of a function or method throughout the codebase. It includes a robust implementation for Go, comprehensive integration tests, and updates to documentation and snapshots to support this new functionality.

New Tool Implementation:

• Added the incoming_calls tool to the MCP server, allowing users to find all callers of a specified function or method. The tool is registered in tools.go and exposes a symbolName parameter for specifying the target symbol.
• Implemented the core logic for finding incoming calls in internal/tools/incoming-calls.go, including symbol resolution, call hierarchy queries, grouping results by file, and context-aware output formatting.

Testing and Snapshots:

• Created comprehensive integration tests in integrationtests/tests/go/incoming_calls/incoming_calls_test.go to validate the tool’s behavior for various symbol types and scenarios (multiple callers, single caller, method callers, and no callers).
• Added snapshot files for test cases, documenting expected outputs for functions with multiple callers, single callers, method callers, and symbols with no callers. [1] [2] [3] [4]

Documentation:

• Updated README.md to include the new incoming_calls tool in the list of available MCP server tools, with a description of its purpose.

Miscellaneous:

• Cleaned up go.mod in the integration test workspace by removing unused dependencies.