Branching system (#10)

This commit enhances the player_monoids library by adding branching support and an improved testing system to make sure it works, as proposed in #9 . These changes enable isolated player state management and improve library reliability. This PR focuses on implementing the branching proposal and adding automated tests.

standard_monoids.lua

@@ -98,7 +98,6 @@ player_monoids.fly = monoid({
 		end
 
 		minetest.set_player_privs(p_name, privs)
-
 	end,
 })
 
@@ -124,30 +123,29 @@ player_monoids.noclip = monoid({
 		end
 
 		minetest.set_player_privs(p_name, privs)
-
 	end,
 })
 
-local def_col_scale = { x=0.3, y=1, z=0.3 }
+local def_col_scale = {x = 0.3, y = 1, z = 0.3}
 
 -- Collisionbox scaling factor. Values are a vector of x, y, z multipliers.
 player_monoids.collisionbox = monoid({
 	combine = v_mult,
-	fold = v_mult_fold({x=1, y=1, z=1}),
-	identity = {x=1, y=1, z=1},
+	fold = v_mult_fold({x = 1, y = 1, z = 1}),
+	identity = {x = 1, y = 1, z = 1},
 	apply = function(multiplier, player)
 		local v = vector.multiply(def_col_scale, multiplier)
 
 		player:set_properties({
-			collisionbox = { -v.x, -v.y, -v.z, v.z, v.y, v.z }
+			collisionbox = {-v.x, -v.y, -v.z, v.z, v.y, v.z}
 		})
 	end,
 })
 
 player_monoids.visual_size = monoid({
 	combine = v_mult,
-	fold = v_mult_fold({x=1, y=1}),
-	identity = {x=1, y=1},
+	fold = v_mult_fold({x = 1, y = 1}),
+	identity = {x = 1, y = 1},
 	apply = function(multiplier, player)
 		player:set_properties({
 			visual_size = multiplier