Adds a treasure chest to the ocean/beach fishing spot. (#85276)

## About The Pull Request
This PR adds a treasure chest that can be fished from the ocean if
you're lucky enough (or have enough explosives or lobstrosities to do it
for you). The treasure chest is basically a mystery box (like the ones
from the deathmatch) with a couple catches; the treasure chest can be
opened up to 18 times in total before breaking down, however, it can
only be opened up to 3 times per spaceman, encouraging the player to
share it with others.

Here the possible loot by the by:
- A toolbox containing a master fishing rod, all the hooks and reels,
fish feed, an experi-scanner, an aquarium kit and a can of super baits
- A box containing a lazarus injector, a cup and a bottle of strange
reagent which you can use to revive fish now
- A circuit board for a pre-emagged fishing portal generator
- A master fishing rod
- A can of super fishing baits
- A fish case containing Tiziran fish
- A fish case containing Syndicate fish
- An old, yet fairly strong cutlass
- An old laser gun which fires only 5 shots before running out
- A crank laser musket
- A smoothbore disabler
- A surplus bolt action rifle
- A ration pack
- A can of squid ink
- A bottle of aged rum that forces you to switch to the piratespeak
language
- A money bag with some doubloons inside
- A piratespeak manual
- Pirate armored coat
- Pirate armored hat
- A pre-loaded cannon
- Four trash cannon balls
- Four cannon balls

## Why It's Good For The Game
Mystery boxes are fun, from the little fanfare they play to the
potential loot they can give, and I had an old treasure chest I had
sprited for fun years ago around so I've come up with an entertaining
idea. If you think the loot list is a bit too hot, I can cool it down a
bit.
Also yeah, I wanted to make fish revivable with strange reagent, since
you can already do it with lazarus injectors even though using a lazarus
injector for this would be a severe waste of mining points.

## Changelog

🆑
add: Added a treasure chest you can rarely fish from the ocean/beach,
with loot being a mix of fishing and piratey stuff.
add: You can revive fish with strange reagent now.
/🆑

code/game/objects/structures/cannons/cannon.dm

@@ -140,5 +140,17 @@
 	new /obj/item/stack/rods(src.loc)
 	. = ..()
 
+///A cannon found from the fishing mystery box.
+/obj/structure/cannon/mystery_box
+	icon_state = "mystery_box_cannon" //east facing sprite for the presented item, it'll be changed back to normal on init
+	dir = EAST
+	anchored = FALSE
+
+/obj/structure/cannon/mystery_box/Initialize(mapload)
+	. = ..()
+	icon_state = "falconet_patina"
+	reagents.add_reagent(/datum/reagent/gunpowder, charge_size)
+	loaded_cannonball = new(src)
+
 #undef BAD_FUEL_DAMAGE_TAX
 #undef BAD_FUEL_EXPLODE_PROBABILTY