Introduce lsp_references tool for enhanced code navigation

[Copilot]

This PR implements the lsp_references tool as requested in issue #11, providing enhanced code navigation capabilities by exposing Neovim's LSP textDocument/references functionality through the MCP interface.

What's New

The new lsp_references tool allows clients to find all references to a symbol at a specific position in a buffer, following the LSP specification for textDocument/references.

Tool Parameters

{
  "connection_id": "string",
  "id": 123,
  "lsp_client_name": "rust_analyzer",
  "line": 10,
  "character": 5,
  "include_declaration": true
}

• connection_id: Unique identifier for the target Neovim instance
• id: Neovim Buffer ID
• lsp_client_name: Name of the LSP client to query
• line/character: Zero-indexed position of the symbol
• include_declaration: Whether to include the symbol's declaration in results

Response Format

Returns an array of Location objects:

[
  {
    "uri": "file:///path/to/file.rs",
    "range": {
      "start": {"line": 5, "character": 10},
      "end": {"line": 5, "character": 15}
    }
  }
]

Implementation Details

The implementation follows the established patterns in the codebase:

1. LSP Integration: Added ReferenceParams and ReferenceContext structs following LSP specification
2. Client Interface: Extended NeovimClientTrait with lsp_references method
3. Lua Script: Created lsp_references.lua for making LSP requests to Neovim
4. MCP Tool: Registered the tool with proper parameter validation and error handling
5. Testing: Added unit tests for parameter serialization and integration test verification

The tool maintains consistency with existing LSP tools (buffer_hover, document_symbols, workspace_symbols) and uses the same connection-aware architecture for multi-instance Neovim support.

Usage Example

# Find all references to a symbol at line 10, character 5 in buffer 1
echo '{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "lsp_references",
    "arguments": {
      "connection_id": "abc123",
      "id": 1,
      "lsp_client_name": "rust_analyzer", 
      "line": 10,
      "character": 5,
      "include_declaration": true
    }
  }
}' | nvim-mcp

This enhancement enables AI assistants and other MCP clients to perform sophisticated code navigation tasks, making it easier to understand code relationships and dependencies across projects.

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