feat(restore): configure circuit breaker

[obacak]

Closes #197

Summary

• expose restore-scoped circuit breaker settings in YAML
• support disabling the Kafka circuit breaker for checkpointed restores
• preserve existing defaults and validate thresholds/timeouts
• add unit/config parsing coverage and documentation

Configuration

restore:
  circuit_breaker:
    enabled: true
    failure_threshold: 15
    reset_timeout_ms: 2000
    success_threshold: 1

cargo test could not be run locally because Rust tooling is unavailable in the environment; language-server diagnostics and git diff --check pass.

[sionsmith]

Thanks for opening this alongside #199 — and for the clear issue report. I've reviewed both: #199 carries the same restore.circuit_breaker settings (plus backup.circuit_breaker, with identical defaults and validation), and additionally documents that the breaker is advisory and fixes the actual cross-partition side effects in the router (global connection-cache clears on any failure) and the per-record mapping lock. I verified those on a 3-broker cluster and approved #199, so I'm closing this one as superseded rather than merging the config-only subset. Details and the end-to-end evidence are in the review on #199.