contrib: add error codes, error hook, latency metrics and rate alert

[wheval]

Summary

Adds reference implementations and tests scoped to contrib/examples/ resolving 4 assigned Wave issues:

1. Standardized Error Codes ([medium] Standardize error code naming convention across SDK modules #249): contrib/examples/standardized-error-codes/
2. Centralized Error Reporting Hook ([easy] Add error reporting hook interface for consumer apps #251): contrib/examples/centralized-error-reporting-hook/
3. RPC Latency Instrumentation ([medium] Add latency instrumentation hooks for rpc.ts calls #252): contrib/examples/rpc-latency-instrumentation/
4. Elevated RPC Error Rate Warning ([medium] Add configurable warning callback for elevated RPC error rate #254): contrib/examples/rpc-elevated-error-rate-warning/

Linked Issues

• Closes [medium] Standardize error code naming convention across SDK modules #249
• Closes [easy] Add error reporting hook interface for consumer apps #251
• Closes [medium] Add latency instrumentation hooks for rpc.ts calls #252
• Closes [medium] Add configurable warning callback for elevated RPC error rate #254

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[github-actions]

Hi @wheval — thanks for the contribution!

We do not accept pull requests to the main branch. All contributions go to the dev branch, so I've automatically retargeted this PR from main to dev for you.

You don't need to reopen anything — your work is preserved and this PR now targets dev. Going forward, please set the base branch to dev when you open a PR. 🙏