feat: Keep track of a min_depth value

Should prevent weird situations where we accidentally gapfill into backfill territory

src/admin/debug/mod.rs

@@ -32,12 +32,6 @@ pub enum DebugCommand {
 		event_id: OwnedEventId,
 	},
 
-	WalkMissingEvents {
-		latest: OwnedEventId,
-		earliest: OwnedEventId,
-		via: String,
-	},
-
 	/// Parse and print a PDU from a JSON
 	///
 	/// The PDU event is only checked for validity and is not added to the