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/modules/admin/verbs/debug.dm

@@ -917,3 +917,41 @@ ADMIN_VERB(queue_tracy, R_DEBUG, "Toggle Tracy Next Round", "Toggle running the
 ADMIN_VERB_CUSTOM_EXIST_CHECK(queue_tracy)
 	return CONFIG_GET(flag/allow_tracy_queue) && fexists(TRACY_DLL_PATH)
 #endif
+
+/datum/mc_dependency_ui
+
+/datum/mc_dependency_ui/ui_interact(mob/user, datum/tgui/ui)
+	ui = SStgui.try_update_ui(user, src, ui)
+	if(!ui)
+		ui = new(user, src, "MCDependencyDebug")
+		ui.set_autoupdate(FALSE)
+		ui.open()
+
+/datum/mc_dependency_ui/ui_state(mob/user)
+	return ADMIN_STATE(R_DEBUG)
+
+/datum/mc_dependency_ui/ui_data(mob/user)
+	var/list/data = list()
+
+	var/list/subsystems = Master.subsystems.Copy()
+	sortTim(subsystems, GLOBAL_PROC_REF(cmp_subsystem_init))
+
+	for(var/datum/controller/subsystem/subsystem as anything in subsystems)
+		var/list/sub_data = list()
+		sub_data["name"] = subsystem.name
+		var/list/dependents = list()
+		for(var/datum/controller/subsystem/dependent as anything in subsystem.dependents)
+			dependents += dependent.name
+		sub_data["dependents"] = dependents
+		data += list(sub_data)
+
+	return list(
+		"subsystems" = data
+	)
+
+/datum/mc_dependency_ui/ui_assets(mob/user)
+	return list(get_asset_datum(/datum/asset/simple/plane_background))
+
+ADMIN_VERB(debug_mc_dependencies, R_DEBUG, "Debug MC Dependencies", "Debug MC dependencies.", ADMIN_CATEGORY_DEBUG)
+	var/datum/mc_dependency_ui/data = new /datum/mc_dependency_ui()
+	data.ui_interact(usr)

code/modules/admin/view_variables/debug_variables.dm

@@ -89,7 +89,10 @@
 		return "<a href='byond://?_src_=vars;[HrefToken()];[link_vars]'>/list ([list_value.len])</a>"
 
 	// if it's a number, is it a bitflag?
-	var/list/valid_bitflags = get_valid_bitflags(name)
+	var/list/valid_bitflags
+	if(!isnum(name))
+		valid_bitflags = get_valid_bitflags(name)
+
 	if(!length(valid_bitflags))
 		return "<span class='value'>[VV_HTML_ENCODE(value)]</span>"