feat(cluster): implement distributed clustering with etcd coordination

- Integrate etcd-client for distributed coordination and leader election
- Add remote client macros with proper formatting for all services
- Implement RequestMetrics for tracking RPC performance and errors
- Add rate limiting mechanism across all service endpoints
- Create ElectionRequest and ElectionResult message types for leader election
- Add role management with primary/replica switching capabilities
- Implement health checker with automatic failover detection
- Add repository count metrics for cluster monitoring
- Update Cargo.toml with etcd-client and dashmap dependencies
- Modify RepoEntry to include read_only flag for replica handling
- Implement should_accept_election logic to prevent duplicate elections
- Add RoleChangedEvent handling for cluster role updates

lib.rs

@@ -4,18 +4,25 @@ pub mod bare;
 pub mod blame;
 pub mod blob;
 pub mod branch;
+pub mod cluster;
 pub mod commit;
 pub mod diff;
+pub mod disk_cache;
 pub mod error;
+pub mod hooks;
 pub mod init;
 pub mod macros;
 pub mod merge;
+pub mod metrics;
 pub mod oid;
+pub mod rate_limit;
 pub mod pack;
+pub mod pack_cache;
 pub mod paginate;
 pub mod pb;
 pub mod refs;
 pub mod sanitize;
 pub mod server;
+pub mod snapshot;
 pub mod tag;
 pub mod tree;