Ports the weather system from Nebula. (#18706)

* part 1

* compiles?

* IT WORKS

* vis contents

* fixes

* umbrelloid

* umbrella 2

* dsasdd

* stuff

* lmao

---------

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/datums/state_machine/state.dm

@@ -0,0 +1,30 @@
+// An individual state, defined as a `/singleton` to save memory.
+// On a directed graph, these would be the nodes themselves, connected to each other by unidirectional arrows.
+/singleton/state
+	// Transition decl types, which get turned into refs to those types.
+	// Note that the order DOES matter, as decls earlier in the list have higher priority
+	// if more than one becomes 'open'.
+	var/list/transitions = null
+
+/singleton/state/Initialize()
+	. = ..()
+	for(var/i in 1 to LAZYLEN(transitions))
+		var/singleton/state_transition/T = GET_SINGLETON(transitions[i])
+		T.from += src
+		transitions[i] = T
+
+// Returns a list of transitions that a FSM could switch to.
+// Note that `holder` is NOT the FSM, but instead the thing the FSM is attached to.
+/singleton/state/proc/get_open_transitions(datum/holder)
+	for(var/singleton/state_transition/T as anything in transitions)
+		if(T.is_open(holder))
+			LAZYADD(., T)
+
+// Stub for child states to modify the holder when switched to.
+// Again, `holder` is not the FSM.
+/singleton/state/proc/entered_state(datum/holder)
+	return
+
+// Another stub for when leaving a state.
+/singleton/state/proc/exited_state(datum/holder)
+	return

code/datums/state_machine/transition.dm

@@ -0,0 +1,16 @@
+// Used to connect `/singleton/state`s together so the FSM knows what state to switch to, and on what conditions.
+// On a directed graph, these would be the arrows connecting the nodes representing states.
+/singleton/state_transition
+	var/list/from = null
+	var/singleton/state/target = null
+
+// Called by one or more state decls acting as nodes in a directed graph.
+/singleton/state_transition/Initialize()
+	. = ..()
+	LAZYINITLIST(from)
+	if(ispath(target))
+		target = GET_SINGLETON(target)
+
+// Tells the FSM if it should or should not be allowed to transfer to the target state.
+/singleton/state_transition/proc/is_open(datum/holder)
+	return FALSE