Add diagnostics and VECTOR index support for Oracle persistence

[Devx228]

Summary

This PR extends the Oracle LangGraph persistence package with operational diagnostics
and expanded Oracle VECTOR support.

It adds read-only diagnostics APIs for both OracleCheckpointSaver and OracleStore,
so users can inspect runtime information, expected tables, migration state, schema
readiness, and VECTOR availability without mutating data.

It also improves OracleStore VECTOR support by adding native VECTOR bind handling when
supported by the installed node-oracledb driver and Oracle Database version, plus
explicit vector index management APIs for creating, listing, and dropping Oracle VECTOR
indexes.

Changes

• Add diagnostics support for Oracle checkpoint and store backends
• Add schema, migration, runtime, and VECTOR readiness inspection
• Add getDiagnostics() to OracleCheckpointSaver
• Add getDiagnostics() to OracleStore
• Add native Oracle VECTOR bind support with fallback behavior
• Add OracleStore vector index create/list/drop APIs
• Export new diagnostics and vector index types
• Add unit coverage for diagnostics behavior
• Expand Oracle integration coverage for VECTOR index management and native vector binds

Testing

• pnpm --filter @oracle/langgraph-oracledb test
• pnpm --filter @oracle/langgraph-oracledb build:internal
• pnpm --filter @oracle/langgraph-oracledb test:int