refactor(cache): redesign cache system with structured keys and improved performance

- Add repo_path parameter to cached_response and cached_vec_response functions
- Implement structured cache key format with namespace, repo_path, and request proto
- Replace global cache with Moka in-memory cache using weight-based eviction
- Set 256MB memory cap with 10-minute TTL and 2-minute TTI policy
- Add metrics collection for cache operations and evictions
- Implement efficient repo-scoped invalidation using key structure
- Add detailed documentation comments explaining cache architecture
- Remove outdated dependencies and update dependency versions
- Add error handling for encoding failures in cache operations
- Optimize Vec responses with length-delimited encoding and pre-allocation

server/repository.rs

@@ -567,9 +567,11 @@ impl repository_service_server::RepositoryService for GitksService {
             .list_snapshots(&repo)
             .map_err(tonic::Status::internal)?;
 
+        let limit = (inner.limit > 0).then_some(inner.limit as usize);
         let resp = ListSnapshotsResponse {
             snapshots: snapshots
                 .into_iter()
+                .take(limit.unwrap_or(usize::MAX))
                 .map(|s| crate::pb::SnapshotInfo {
                     snapshot_id: s.snapshot_id,
                     relative_path: s.relative_path,
@@ -678,7 +680,7 @@ impl repository_service_server::RepositoryService for GitksService {
                 return;
             }
             for offset in (0..total).step_by(CHUNK_SIZE) {
-                let end = (offset + CHUNK_SIZE).min(total);
+                let end = offset.saturating_add(CHUNK_SIZE).min(total);
                 let chunk_data = bundle_data[offset..end].to_vec();
                 let is_done = end >= total;
                 if tx