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- Remove outdated dependencies and update dependency versions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

merge/do_merge.rs

@@ -7,7 +7,10 @@ impl GitBare {
         let target_branch = request.target_branch.clone();
         crate::sanitize::validate_ref_name(&target_branch)?;
         let source_revision = match request.source.and_then(|s| s.selector) {
-            Some(crate::pb::object_selector::Selector::Oid(oid)) => oid.hex.clone(),
+            Some(crate::pb::object_selector::Selector::Oid(oid)) => {
+                crate::sanitize::validate_oid_hex(&oid.hex)?;
+                oid.hex.clone()
+            }
             Some(crate::pb::object_selector::Selector::Revision(name)) => {
                 crate::sanitize::validate_revision(&name.revision)?;
                 name.revision.clone()