Refactors subsystems to use dependency-ordering to determine init order. Subsystems can now declare their own dependencies. (#90268)

## About The Pull Request
As the title says.
`init_order` is no more, subsystems ordering now depends on their
declared dependencies.
Subsystems can now declare which other subsystems need to init before
them using a list and the subsystem's typepath
I.e.
```dm
dependencies = list(
    /datum/controller/subsystem/atoms,
    /datum/controller/subsystem/mapping
)
```
The reverse can also be done, if a subsystem must initialize after your
own:
```dm
dependents = list(
    /datum/controller/subsystem/atoms
)
```
Cyclical dependencies are not allowed and will throw an error on
initialization if one is found.
There's also a debug tool to visualize the dependency graph, although
it's a bit basic:

![image](https://github.com/user-attachments/assets/80c854d9-c2a5-4f2f-92db-a031e9a8e257)

Subsystem load ordering can still be controlled using `init_stage`, some
subsystems use this in cases where they must initialize first or last
regardless of dependencies. An error will be thrown if a subsystem has
an `init_stage` before one of their dependencies.

## Why It's Good For The Game
Makes dealing with subsystem dependencies easier, and reduces the chance
of making a dependency error when needing to shift around subsystem
inits.

## Changelog
🆑
refactor: Refactored subsystem initialization
/🆑

code/controllers/subsystem/processing/ai_behaviors.dm

@@ -4,7 +4,9 @@ PROCESSING_SUBSYSTEM_DEF(ai_behaviors)
 	flags = SS_POST_FIRE_TIMING|SS_BACKGROUND
 	priority = FIRE_PRIORITY_NPC_ACTIONS
 	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
-	init_order = INIT_ORDER_AI_CONTROLLERS
+	dependencies = list(
+		/datum/controller/subsystem/movement/ai_movement
+	)
 	wait = 1
 	///List of all ai_behavior singletons, key is the typepath while assigned value is a newly created instance of the typepath. See SetupAIBehaviors()
 	var/list/ai_behaviors

code/controllers/subsystem/processing/ai_idle_behaviors.dm

@@ -3,7 +3,9 @@ PROCESSING_SUBSYSTEM_DEF(idle_ai_behaviors)
 	flags = SS_BACKGROUND
 	wait = 1.5 SECONDS
 	priority = FIRE_PRIORITY_IDLE_NPC
-	init_order = INIT_ORDER_AI_IDLE_CONTROLLERS //must execute only after ai behaviors are initialized
+	dependencies = list(
+		/datum/controller/subsystem/ai_controllers
+	)
 	///List of all the idle ai behaviors
 	var/list/idle_behaviors = list()
 

code/controllers/subsystem/processing/fishing.dm

@@ -1,6 +1,9 @@
 /// subsystem for the fishing minigame processing.
 PROCESSING_SUBSYSTEM_DEF(fishing)
 	name = "Fishing"
+	dependencies = list(
+		/datum/controller/subsystem/atoms
+	)
 	flags = SS_BACKGROUND
 	wait = 0.05 SECONDS // If you raise it to 0.1 SECONDS, you better also modify [datum/fish_movement/move_fish()]
 	///A list of cached fish icons

code/controllers/subsystem/processing/greyscale.dm

@@ -7,9 +7,8 @@
 PROCESSING_SUBSYSTEM_DEF(greyscale)
 	name = "Greyscale"
 	flags = SS_BACKGROUND
-	init_order = INIT_ORDER_GREYSCALE
 	wait = 3 SECONDS
-
+	init_stage = INITSTAGE_EARLY
 	var/list/datum/greyscale_config/configurations = list()
 	var/list/datum/greyscale_layer/layer_types = list()
 #ifdef USE_RUSTG_ICONFORGE_GAGS

code/controllers/subsystem/processing/instruments.dm

@@ -1,7 +1,6 @@
 PROCESSING_SUBSYSTEM_DEF(instruments)
 	name = "Instruments"
 	wait = 0.5
-	init_order = INIT_ORDER_INSTRUMENTS
 	flags = SS_KEEP_TIMING
 	priority = FIRE_PRIORITY_INSTRUMENTS
 	/// List of all instrument data, associative id = datum

code/controllers/subsystem/processing/quirks.dm

@@ -47,7 +47,6 @@ GLOBAL_LIST_INIT(quirk_string_blacklist, generate_quirk_string_blacklist())
 // - Quirk datums are stored and hold different effects, as well as being a vector for applying trait string
 PROCESSING_SUBSYSTEM_DEF(quirks)
 	name = "Quirks"
-	init_order = INIT_ORDER_QUIRKS
 	flags = SS_BACKGROUND
 	runlevels = RUNLEVEL_GAME
 	wait = 1 SECONDS

code/controllers/subsystem/processing/reagents.dm

@@ -2,11 +2,11 @@
 
 PROCESSING_SUBSYSTEM_DEF(reagents)
 	name = "Reagents"
-	init_order = INIT_ORDER_REAGENTS
 	priority = FIRE_PRIORITY_REAGENTS
 	wait = 0.25 SECONDS //You might think that rate_up_lim has to be set to half, but since everything is normalised around seconds_per_tick, it automatically adjusts it to be per second. Magic!
 	flags = SS_KEEP_TIMING
 	runlevels = RUNLEVEL_GAME | RUNLEVEL_POSTGAME
+	init_stage = INITSTAGE_EARLY
 	///What time was it when we last ticked
 	var/previous_world_time = 0
 

code/controllers/subsystem/processing/station.dm

@@ -1,6 +1,5 @@
 PROCESSING_SUBSYSTEM_DEF(station)
 	name = "Station"
-	init_order = INIT_ORDER_STATION
 	flags = SS_BACKGROUND
 	runlevels = RUNLEVEL_GAME
 	wait = 5 SECONDS