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/ai/basic_mobs/basic_subtrees/speech_subtree.dm

@@ -185,6 +185,11 @@
 	emote_see = list("shakes their head.", "shivers.")
 	speak = list("Ack-Ack", "Ack-Ack-Ack-Ackawoooo", "Geckers", "Awoo", "Tchoff")
 
+/datum/ai_planning_subtree/random_speech/crab
+	speech_chance = 1
+	emote_hear = list("clicks.")
+	emote_see = list("clacks.")
+
 /datum/ai_planning_subtree/random_speech/penguin
 	speech_chance = 5
 	speak = list("Gah Gah!", "NOOT NOOT!", "NOOT!", "Noot", "noot", "Prah!", "Grah!")