fix: failover scenarios

[loks0n]

• Rename State->save() and State->saveAll() to State->set() and State->setAll() for clarity
• Circuit breaker logic to proxied requests, marking executors and runtimes as unhealthy when cURL errors are encountered.
• /v1/proxy/stats endpoint for monitoring
• Exhaustive exception catching in the healthcheck loop to prevent exceptions bringing down all executors