Add TimeProvider-based timing to SafeFileCache crash-loop bypass

[mattklein123]

Summary

This updates SafeFileCache to use bd_time::TimeProvider for crash-loop timeout logic and makes the 4-hour same-nonce bypass deterministic in tests.

Changes

• Add TimeProvider injection to SafeFileCache via new_with_time_provider(...) while keeping new(...) on SystemTimeProvider.
• Persist and evaluate last_successful_cache_at using provider-backed wall clock in crash-loop guard decisions.
• Update safe_file_cache_test.rs to use TestTimeProvider and strengthen assertions around retry reset and guard re-engagement.
• Thread provider-aware constructors through bd-runtime and bd-logger (ConfigLoader::new_with_time_provider, Config::new_with_time_provider, and builder wiring).
• Update bd-client-common/AGENTS.md with full algorithm details for TimeProvider-based behavior and bypass flow.