Add Support for the #set! directive and #is? predicate

[DavidBakerEffendi]

This change introduces support for the #set! directive and #is? predicate within Tree-sitter queries. These additions allow users to associate arbitrary key-value metadata with query matches and perform conditional checks against that metadata.

Key changes include:

• TSQueryMatch: Added a metadata map to store key-value pairs.
• TSQueryCursor: Updated nextMatch and nextCapture to clear metadata between iterations, ensuring match isolation.
• TSQueryPredicate: Implemented TSQueryPredicateSet and TSQueryPredicateIs logic.
• TSQuery: Added internal handlers to parse and initialize these new predicate types from query source strings.
• Optimization: Refactored getStringValueForId in TSQuery for direct lookup by ID, improving performance.
• Tests: Added TSQueryMetadataTest to verify metadata persistence, isolation, and predicate logic.

Resolves #130