Fully fixes atom init desyncs (#76179)

## About The Pull Request

The old system was... ok, but the stack trace was unfortuante, and the
potential to double remove was silly.
Let's use a list of source, value instead, to block overremovals and
properly support different load states

## Why It's Good For The Game

Prevents a bug a goodhearted bagilmin showed me where shuttles would
randomly just fail to load.
Calling clear twice should not be a failure

## Changelog
🆑
fix: Maps loaded post init will no longer randomly enter a failed state.
Hopefully.
/🆑

code/modules/mapping/reader.dm

@@ -249,9 +249,9 @@
 
 #define MAPLOADING_CHECK_TICK \
 	if(TICK_CHECK) { \
-		SSatoms.map_loader_stop(); \
+		SSatoms.map_loader_stop(REF(src)); \
 		stoplag(); \
-		SSatoms.map_loader_begin(); \
+		SSatoms.map_loader_begin(REF(src)); \
 	}
 
 // Do not call except via load() above.
@@ -259,7 +259,7 @@
 	PRIVATE_PROC(TRUE)
 	// Tell ss atoms that we're doing maploading
 	// We'll have to account for this in the following tick_checks so it doesn't overflow
-	SSatoms.map_loader_begin()
+	SSatoms.map_loader_begin(REF(src))
 
 	// Loading used to be done in this proc
 	// We make the assumption that if the inner procs runtime, we WANT to do cleanup on them, but we should stil tell our parents we failed
@@ -272,7 +272,7 @@
 			sucessful = _dmm_load(x_offset, y_offset, z_offset, cropMap, no_changeturf, x_lower, x_upper, y_lower, y_upper, placeOnTop, new_z)
 
 	// And we are done lads, call it off
-	SSatoms.map_loader_stop()
+	SSatoms.map_loader_stop(REF(src))
 
 	if(new_z)
 		for(var/z_index in bounds[MAP_MINZ] to bounds[MAP_MAXZ])
@@ -409,7 +409,7 @@
 
 			var/list/cache = modelCache[gset.gridLines[i]]
 			if(!cache)
-				SSatoms.map_loader_stop()
+				SSatoms.map_loader_stop(REF(src))
 				CRASH("Undefined model key in DMM: [gset.gridLines[i]]")
 			build_coordinate(cache, locate(true_xcrd, ycrd, zcrd), no_afterchange, placeOnTop, new_z)
 
@@ -542,7 +542,7 @@
 					continue
 				var/list/cache = modelCache[model_key]
 				if(!cache)
-					SSatoms.map_loader_stop()
+					SSatoms.map_loader_stop(REF(src))
 					CRASH("Undefined model key in DMM: [model_key]")
 				build_coordinate(cache, locate(xcrd, ycrd, zcrd), no_afterchange, placeOnTop, new_z)
 
@@ -956,6 +956,7 @@ GLOBAL_LIST_EMPTY(map_model_default)
 
 /datum/parsed_map/Destroy()
 	..()
+	SSatoms.map_loader_stop(REF(src)) // Just in case, I don't want to double up here
 	if(turf_blacklist)
 		turf_blacklist.Cut()
 	parsed_bounds.Cut()