test: add comprehensive real-world schema pattern tests (#412)

Add 58 new tests across 5 test suites covering common JSON Schema patterns found in production:
- OpenAPI 3.0 patterns (allOf, oneOf, anyOf composition, extended $refs)
- Recursive data structures (linked lists, trees, graphs, AST patterns)
- JSON Schema Draft 7 advanced features (if/then/else, $defs, patternProperties)
- Complex schema composition (diamond patterns, Kubernetes-style deep nesting)
- Edge cases and options (mutateInputSchema, excludedPathMatcher, callbacks)

All tests pass. Coverage includes real-world patterns from OpenAPI specs, Kubernetes
definitions, GraphQL schemas, and configuration file patterns like VS Code settings.

Author: jonluca