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/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>"