Fixes Modular Map Loading Runtimes (#64212)

## About The Pull Request

Moves the modmap root object's load_map() call to New(). This changes something about where it falls in init order that stops it from causing a flood of lighting runtimes. Don't ask my why, it just does.

## Why It's Good For The Game

Fixes #64192

code/modules/mapping/modular_map_loader/modular_map_loader.dm

@@ -11,6 +11,8 @@
 	/// Key used to look up the appropriate map paths in the associated .toml file
 	var/key = null
 
+INITIALIZE_IMMEDIATE(/obj/modular_map_root)
+
 /obj/modular_map_root/Initialize(mapload)
 	. = ..()
 	INVOKE_ASYNC(src, .proc/load_map)