Add in-depth duration measuring for code owner approval methods

Marc Shawrequested to merge
duo-edit-20251223-195216 into master

What does this MR do and why?

This MR reintroduces performance instrumentation to measure the duration of code owner approval operations in MergeRequests::ResetApprovalsService, with more granular sub-operation measurements than the previous implementation.

The instrumentation is behind the log_merge_request_reset_approvals_duration feature flag and logs detailed timing data to help identify performance bottlenecks in the code owner approval reset flow.

Metrics Logged

Metric Description
delete_code_owner_approvals_total_duration_s Total time for the entire code owner deletion flow
find_approved_code_owner_rules_total_duration_s Time to find code owner rules with approved approvers
code_owner_approver_ids_to_delete_total_duration_s Total time for approver ID extraction
code_owner_approver_ids_previous_diff_sha_duration_s Time to get previous diff SHA
code_owner_approver_ids_entries_since_commit_duration_s Time for CodeOwners.entries_since_merge_request_commit
code_owner_approver_ids_match_rules_duration_s Time to match rules and extract IDs
code_owner_approver_ids_filter_approvals_duration_s Time to filter approvals by user IDs
perform_code_owner_approval_deletion_total_duration_s Total time for the deletion operation
perform_deletion_check_approval_state_duration_s Time to check if MR was approved
perform_deletion_delete_all_duration_s Time for the actual delete_all query
perform_deletion_expire_keys_duration_s Time to expire cache keys
perform_deletion_update_reviewer_state_duration_s Time to update reviewer states
perform_deletion_trigger_events_duration_s Time for internal event triggers
perform_deletion_webhooks_duration_s Time for webhook execution
reset_approvals_service_total_duration_s Sum of all measured durations

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