Converting crabs to basic mobs (#77109)

## About The Pull Request
Exactly what it reads on the tin. As a bonus, they will flee from
attacking targets, hunt tiny critters (crabs are now small-sized) and
actually move sideways (it's an element that covers both client and
basic movement)


## Why It's Good For The Game
Another simple to basic mob refactor.

## Changelog

🆑
refactor: Crabs refactored into basic mobs. They now hunt tiny critters
and flee from attackers.
fix: Fixed crabs not crab-walking.
/🆑

code/datums/memory/_memory.dm

@@ -253,6 +253,7 @@
 		/mob/living/basic/chicken,
 		/mob/living/basic/cow,
 		/mob/living/basic/cow/wisdom,
+		/mob/living/basic/crab,
 		/mob/living/basic/giant_spider,
 		/mob/living/basic/giant_spider/hunter,
 		/mob/living/basic/mining/goliath,
@@ -268,7 +269,6 @@
 		/mob/living/basic/statue,
 		/mob/living/basic/stickman,
 		/mob/living/basic/stickman/dog,
-		/mob/living/simple_animal/crab,
 		/mob/living/simple_animal/hostile/asteroid/basilisk/watcher,
 		/mob/living/simple_animal/hostile/bear,
 		/mob/living/simple_animal/hostile/blob/blobbernaut/independent,