Feat: add resilient subscription helpers with reconnection and gap recovery

[MayurK-cmd]

Add createResilientSubscription and coordinateSubscriptionRecovery utilities to help applications build robust WebSocket subscriptions that automatically reconnect on failure and recover from message gaps.

createResilientSubscription wraps a subscription factory with:

• Automatic reconnection on failure
• Exponential backoff with jitter (configurable)
• Optional message gap recovery via onGap callback
• AbortSignal support for graceful shutdown
• Async generator interface for streaming results

coordinateSubscriptionRecovery runs multiple recovery functions in parallel and collects any errors, useful for synchronizing catch-up logic across multiple subscriptions after network failures.

Both utilities include comprehensive JSDoc with usage examples and follow Kit conventions (functional composition, TypeScript strict mode, proper error handling).

Closes #1990

Testing: Manual integration tests conducted - all 4 test scenarios pass:

• Test 1: Basic reconnection with gap recovery ✓
• Test 2: Parallel recovery coordination ✓
• Test 3: AbortSignal handling ✓
• Test 4: Edge case (empty recovery functions) ✓

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Latest commit: 5a5883a

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[mcintyre94]

Thanks for this, but my instinct is that this it too opinionated for Kit. It's definitely too opinionated for packages/rpc-subscriptions. If we did add something like this then we'd probably want it in packages/kit, which is where the higher-level more opinionated functionality lives. But then we'd be positioning this as the default, and that needs some careful design thought from us.

I think this may be better off as an independent package outside of Kit, perhaps published as a Kit Plugin.

[MayurK-cmd]

Thanks for the feedback! Makes sense — I'll publish this as a community plugin instead and open a PR to kit-plugins to get it listed in the Community Plugins table. Appreciate the pointer to that repo.