Refactors projectile ricochets (#25764)

* same taste, twice the speed

* pulls proc/handle_ricochet() to the atom level. adds var/flags_ricochet and related defines.

* space indentation sneaks its way in yet again

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Co-authored-by: Luc <89928798+lewcc@users.noreply.github.com>

code/game/objects/structures.dm

@@ -3,6 +3,8 @@
 	pressure_resistance = 8
 	max_integrity = 300
 	face_while_pulling = TRUE
+	flags_ricochet = RICOCHET_HARD
+	receive_ricochet_chance_mod = 0.6
 	var/climbable
 	/// Determines if a structure adds the TRAIT_TURF_COVERED to its turf.
 	var/creates_cover = FALSE