Issue #128 Refactor JsonPath to sealed interface with AST interpreter

Refactoring to prepare for runtime compilation support:
- JsonPath is now a sealed interface permitting JsonPathInterpreted and JsonPathCompiled
- JsonPathInterpreted contains the existing AST-walking evaluation logic
- JsonPathCompiled stub added for future bytecode-compiled implementation
- JsonPathCompiler stub added with in-memory compilation infrastructure
- All 100 existing tests pass unchanged

Next steps: Add tests and implementation for runtime-compiled JsonPath

Co-authored-by: simbo1905 <simbo1905@60hertz.com>

Author: cursoragent