Add comprehensive tree-sitter highlighting with Neovim parser integration

[Copilot]

Working on integrating with nvim-treesitter parsers as requested in feedback.

Progress

• [x] Analyze current tree-sitter implementation that uses static parser dependencies
• [x] Research nvim-treesitter parser integration approach
• [x] Modify tree-sitter implementation to use nvim-treesitter's installed parsers dynamically
• [x] Make tree-sitter language parsers optional dependencies in Cargo.toml
• [x] Add feature flags: builtin-parsers (default) and nvim-treesitter-only
• [x] Use conditional compilation to reduce dependency footprint when needed
• [x] Update parser loading logic to check for nvim-treesitter availability first
• [x] Add helpful error messages when parsers are missing
• [x] Test both feature configurations (builtin and nvim-treesitter-only)
• [x] Update documentation with new integration options
• [ ] Reply to the user's comment

Changes Made

Cargo.toml

• Made all tree-sitter language parsers optional dependencies
• Added builtin-parsers feature (enabled by default) that includes all static parsers
• Added nvim-treesitter-only feature for users who want to rely entirely on nvim-treesitter
• Reduced dependency footprint when using --no-default-features

Tree-sitter Integration

• Added check_nvim_treesitter_parser() to verify parser availability in nvim-treesitter
• Modified load_nvim_treesitter_parser() to check nvim-treesitter first, then fallback to static parsers
• Used conditional compilation (#[cfg(feature = "...")]) to only include static parsers when enabled
• Improved error messages that guide users to install parsers via :TSInstall or enable features

Documentation

• Updated README.md with comprehensive nvim-treesitter integration documentation
• Documented both build options: default (builtin-parsers) and nvim-treesitter-only
• Added supported languages list and error message explanations
• Included build instructions for different configurations

Benefits

• Reduced Dependencies: Users can now build without static parsers using --no-default-features
• nvim-treesitter Integration: Checks if parsers are available in user's nvim-treesitter installation
• Smart Fallbacks: Uses static parsers when nvim-treesitter is unavailable
• Better Error Messages: Clear guidance on how to install missing parsers
• Backward Compatibility: Default behavior unchanged (includes builtin parsers)

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