Add a unit test to check that maploaded simple/basic mobs are in an environment they can survive in. (#82180)

## About The Pull Request
I've recently noticed that the maploaded penguins from the snowdin away
mission were dying from unsafe atmos/temperature. This sparked the idea
of making a (focus only) unit test that would prevent this sort of
issues from happening.

This PR also implements the usage of the `atmos_requirements` and
`body_temp_sensitive` elements for simple animals too, cutting down the
copypaste.

## Why It's Good For The Game
More unit tests to make sure things are done correctly.

## Changelog

🆑
fix: Made sure that mapped critters (i.e. penguins on the snow cabin
away mission) can survive in the environment they're spawned in.
/🆑

code/controllers/subsystem/dcs.dm

@@ -57,7 +57,7 @@ PROCESSING_SUBSYSTEM_DEF(dcs)
 	var/datum/element/eletype = arguments[1]
 	var/list/fullid = list(eletype)
 	var/list/named_arguments
-	for(var/i in initial(eletype.argument_hash_start_idx) to length(arguments))
+	for(var/i in initial(eletype.argument_hash_start_idx) to (initial(eletype.argument_hash_end_idx) || length(arguments)))
 		var/key = arguments[i]
 
 		if(istext(key))