Retry transient informer failures

[brendandburns]

Summary

• retry transient informer LIST and WATCH failures instead of terminating the informer
• classify network errors, HTTP 408, 429, and 5xx responses as retryable while preserving terminal behavior for other 4xx errors
• reuse the existing client-go-inspired exponential jittered backoff and preserve timeout, 410 Gone, and explicit-stop behavior
• add deterministic regression coverage for retryable LIST/WATCH failures and clean informer shutdown

This addresses the P0 informer recovery gap identified in the client-go gap analysis.

Testing

• npm run build
• node --test --test-reporter=spec --import tsx src/cache_test.ts
• full repository test suite: 361 passed, 0 failed
• repository push hooks

[kubernetes-prow]

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This pull-request has been approved by: brendandburns

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