Draft: feat: preload merge_request_commits_metadata association

Relates to issue #527235

This MR was created by Duo in Session 1108236

Changes

• Add preloading for merge_request_commits_metadata association to reduce N+1 SQL queries
• Update MergeRequest.preload_latest_diff_commit to include commit metadata preloading
• Optimize MergeRequest#recent_commits with conditional preloading
• Enhance MergeRequestDiff#commit_shas to prevent N+1 queries when accessing SHA data
• Update MergeRequest#committers to preload user information efficiently
• Optimize Banzai::Filter::References::MergeRequestReferenceFilter#find_commit_by_sha for commit lookups
• Ensure plan-time partition pruning by including project_id in preload conditions