feat: support mongo as a external store

[wichopy]

This is me trying to do some vibe coding. I saw redis and dynamo db were supported so wanted to see if I could get mongo in here. Feel free to close this PR or help me take it all the way :D

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• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

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Note

Introduces a new MongoDB-backed feature store and big segment store with connection management, caching, factories, tests, and documentation.

• New package: packages/store/node-server-sdk-mongodb
  • Provides MongoDB-backed persistence for the Node.js Server-Side SDK.
• Stores:
  • MongoDBFeatureStore: Persistent feature/segment storage using MongoDB with versioned upserts and delete handling.
  • MongoDBBigSegmentStore: Big segment metadata and user membership retrieval.
• Core/State:
  • MongoDBCore: Implements PersistentDataStore operations (init/get/getAll/upsert/initialized) against MongoDB collections.
  • MongoDBClientState: Connection handling with URI/database/prefix support, retry logic, and collection prefixing.
• Factories & API:
  • MongoDBFeatureStoreFactory and MongoDBBigSegmentStoreFactory; re-exported as MongoDBFeatureStore and MongoDBBigSegmentStore from src/index.ts.
  • LDMongoDBOptions for configuration (uri, database, prefix, timeouts, retries, cacheTTL); TtlFromOptions for cache TTL.
• Tests:
  • Comprehensive unit/integration tests for feature store, big segment store, client state, and factories (Jest + ts-jest).
• Configs & Docs:
  • README.md with setup/usage, CHANGELOG.md, package.json, Jest/TypeScript configs; Apache-2.0 LICENSE.

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[kinyoklion]

Hello @wichopy,

Thank you for the contribution. Is this something you were going to be using, or only created for exploratory purposes?

Generally speaking each feature is associated with maintenance, and that maintenance burden will only be worth consideration if there are people in active need of the feature.

Thank you,
Ryan

[wichopy]

Hello @wichopy,

Thank you for the contribution. Is this something you were going to be using, or only created for exploratory purposes?

Generally speaking each feature is associated with maintenance, and that maintenance burden will only be worth consideration if there are people in active need of the feature.

Thank you,

Ryan

It was something my company wanted to use as dynamo and redis were not viable options. I figured there maybe more people wanting this as mongo is pretty popular.

I agree maintenance is a valid concern. I wanted to just get feature parity with the other supported external stores with the help of AI.