Add production-ready Elasticsearch query processor

Implement a comprehensive Elasticsearch query processor that transforms
ActiveContext::Query AST nodes into Elasticsearch DSL queries. This
implementation provides proper handling of all query types and follows
best practices for query composition.

Key changes:
- Add Processor class with support for filter, prefix, knn, and boolean queries
- Implement helper methods for consistent query building
- Add comprehensive test coverage
- Add YARD documentation for all methods

Details:
* Processor changes:
  - Implement transform method following concern contract
  - Add build_bool_query helper for consistent query construction
  - Add proper handling of KNN queries with other conditions
  - Implement proper query composition for nested structures

* Test improvements:
  - Add comprehensive test suite with all query types
  - Add test cases for complex nested queries
  - Add edge case coverage
  - Use shared examples for common query patterns

* Documentation:
  - Add YARD documentation for all public methods
  - Add usage examples
  - Document query composition patterns
  - Add type specifications for parameters

This implementation provides a production-ready solution for transforming
query AST nodes into Elasticsearch queries, with proper handling of all
supported query types and edge cases.