[mikemikimike]

Fixes #631

Issue: #631

Summary

• Add NativeAOT-friendly dynamic vector collection operations for document loading, insertion, retrieval by ID, and similarity search.
• Use source-generated JSON metadata for JSON-compatible values while retaining the reflection fallback on JIT. Unsupported POCO metadata fails clearly when reflection is disabled; the existing typed API remains available for JIT and is marked as requiring dynamic code on supported targets.
• Update the Chroma sample with a smoke path that checks upsert, read, metadata round-trip, and similarity search.
• Keep writes sequential per record, matching the existing typed API; a provider failure during a batch can leave earlier records written. Concurrent writers were not stress-tested.

Validation

• .NET 10.0.400 Core multi-target build and Chroma sample build passed.
• Focused vector metadata tests passed (2/2).
• Windows NativeAOT publish passed. The Chroma 1.5.9 round-trip smoke passed in both NativeAOT and JIT modes.
• The full solution test run reports failures in the existing TextLoaderTest and Excel tests. Both failures were reproduced on unmodified upstream commit 4d80626 using the same .NET 10.0.400 container.

[CLAassistant]

All committers have signed the CLA.

[HavenDV]

Reviewed the complete vector mapping, metadata serialization, sample, and regression-test changes. The contribution preserves the typed API and its POCO serialization behavior while adding an explicit dynamic-record path for NativeAOT.

Validated the combined changes locally on macOS arm64: full solution Release build (zero errors; existing warnings remain), 42 core tests, 8 splitter abstraction tests, and 2 C# splitter tests passed. Published a real NativeAOT Chroma sample with reflection disabled and executed its synthetic-embedding upsert/read/metadata/search smoke against loopback-only Chroma 1.5.9; it passed. No provider endpoint or paid API was invoked.

The reviewed source files are unchanged by the subsequent merges from main. Current-main SQLite follow-up 68e3613 also covers LocalRAG. Awaiting the refreshed required CI check before merging. Existing unrelated LangChain reflection/AOT warnings and advisories are not claims of full-library NativeAOT compatibility.