Adds snakes to the game. (#21185)

Ports the snake from Baystation over to Aurora.

No snakes have been placed ingame, but they're on the Technomancer
"Summon Creature" list and the Random Animal Crate object has a chance
to spawn a snake crate.

All credit for the snake, snake_m, and snake_dead sprites goes to
Baystation. I modified the original sprite to create the snake_rest
sprite.

---------

Signed-off-by: ASmallCuteCat <neofelisnebulosa128@gmail.com>
Co-authored-by: FlamingLily <80451102+FlamingLily@users.noreply.github.com>

code/modules/mob/living/simple_animal/friendly/snake.dm

@@ -0,0 +1,18 @@
+/mob/living/simple_animal/snake
+	name = "snake"
+	desc = "A slithering serpent."
+	icon_state = "snake"
+	icon_living = "snake"
+	icon_dead = "snake_dead"
+	icon_rest = "snake_rest"
+	speak_emote = list("hisses")
+	emote_see = list("flicks out its tongue", "looks around")
+	health = 15
+	maxHealth = 15
+	organ_names = list("head", "body")
+	response_help  = "pets"
+	response_disarm = "boops"
+	response_harm   = "stomps on"
+	mob_size = MOB_SMALL
+	canbrush = TRUE
+	brush = /obj/item/reagent_containers/glass/rag