Add PG 17 / 18 Support

[Vonng]

• FDW Path API Evolution: Extended create_foreignscan_path wrapper to accommodate new parameters—fdw_restrictinfo (PG17) and disabled_nodes (PG18). Version-specific macro
  definitions pass appropriate defaults (NIL and 0 respectively) to satisfy the new signatures.
• JSON Subsystem Refactoring: PG17 internalized JSON processing functions with modified signatures. Implemented compatibility wrappers for json_categorize_type (now
  requires boolean parameter) and datum_to_json (return type changed from void to Datum). Pre-17 versions retain original static implementations.
• Lexer Initialization Contract Change: Adapted makeJsonLexContextCstringLen invocation to use stack-allocated JsonLexContext buffer for PG17+, replacing the previous
  heap-allocation model.
• Tuplestore API Cleanup: Removed tuplestore_donestoring call for PG17+ where explicit finalization is no longer necessary.
• Header Modularization: Added explicit includes for explain_state.h and explain_format.h in PG18, following the reorganization of explain infrastructure.
• Type Qualifier Corrections: Updated save_json_start member to const char* matching PG17's stricter const-correctness requirements.

[rapimo]

Hey @Vonng thanks for the changes, I put them into #51