fix(replication): persist delete marker mtime in MRF entries (#4331)

fix(replication): persist original mtime in MRF entries (backlog#867)

MRF delete entries did not persist the original delete-marker mtime, so
after a restart the recovery replay path reconstructed the delete without
a source timestamp. Downstream the replica delete-marker was stamped with
the replay time (now()) instead of the source mtime, causing delete-marker
timestamp divergence across clusters.

Extend the MrfReplicateEntry disk format with an optional deleteMarkerMtime
field (persisted as Unix nanoseconds) in both duplicate struct definitions
(rustfs-replication and rustfs-filemeta). DeletedObjectReplicationInfo now
persists delete_marker_mtime, and start_mrf_processor restores it onto the
reconstructed delete so the replica keeps the source timestamp.

Backward compatibility: the new key uses skip_serializing_if + serde
default, so historical MRF files without it decode to None and replay
falls back to the current time (pre-#867 behaviour). No panic or entry
loss on old files.

Closes rustfs/backlog#867

crates/filemeta/src/replication.rs

@@ -586,6 +586,13 @@ pub struct MrfReplicateEntry {
     // Old files lack this; default=false is correct.
     #[serde(rename = "deleteMarker", default)]
     pub delete_marker: bool,
+
+    // For delete entries: the original delete-marker mtime, persisted as Unix nanoseconds so
+    // replay stamps replicas with the source timestamp instead of the replay time. Old files
+    // lack this key; default=None means "unknown", and replay falls back to the current time
+    // to preserve pre-existing behaviour (backlog#867).
+    #[serde(rename = "deleteMarkerMtime", skip_serializing_if = "Option::is_none", default)]
+    pub delete_marker_mtime: Option<i64>,
 }
 
 pub trait ReplicationWorkerOperation: Any + Send + Sync {
@@ -787,6 +794,7 @@ impl ReplicationWorkerOperation for ReplicateObjectInfo {
             op: MrfOpKind::Object,
             delete_marker_version_id: None,
             delete_marker: false,
+            delete_marker_mtime: None,
         }
     }
 
@@ -837,6 +845,7 @@ impl ReplicateObjectInfo {
             op: MrfOpKind::Object,
             delete_marker_version_id: None,
             delete_marker: false,
+            delete_marker_mtime: None,
         }
     }
 }