Fix pride pin reskinning (#82920)

## About The Pull Request

**Edit: Since writing, this pr has been updated to address failing CI
based on code-general suggestions, invalidating the previous
descriptions. The previous descriptions has been included as spoilers
for posterity**

Right, so, this has gone from just a simple pride pin fix to realizing
CI fails with it to doing a more complex lasting fix based on
suggestions.

Recap time. Objects get reskinning set up if they have `unique_reskin`
set when `Initialize(...)` runs.

https://github.com/tgstation/tgstation/blob/9145ecb7e1e44635a1056fc704adfa3d764325e6/code/game/objects/items.dm#L267-L269
Because pride pins use a global list, we set it in `Initialize(...)`...
After we call the parent.

https://github.com/tgstation/tgstation/blob/9145ecb7e1e44635a1056fc704adfa3d764325e6/code/modules/clothing/under/accessories/badges.dm#L196-L198
Obviously this fails.

However, moving this *before* `Initialize(...)`, while fixing the issue,
causes CI to fail due to calling `register_context()` twice.
Why? Well, it's simple. We automatically call `register_context()` if we
have `unique_reskin` set, as seen above, but we *also* call it on
accessory `Initialize(...)` due to it having its own context.

https://github.com/tgstation/tgstation/blob/0c562fd74299f8ce92a81c0a932b8ec4862189af/code/modules/clothing/under/accessories/_accessories.dm#L29-L31
This causes it to try register the same thing twice, which doesn't
_break_ things, but it sure as hell isn't clean.

So talking about this with San in code general, we decided to try go
with the following:
We add two new procs, `setup_reskinning()` and
`check_setup_reskinning()`, and handle all this fuckery within those.
This lets subtypes override them with their own new checks or
differences in setup.
Then we override `setup_reskinning()` for `/obj/item/clothing/under` and
`/obj/item/clothing/accessory` to not register context again, and do the
same for `/obj/item/clothing/accessory/pride` but while also setting
`unique_reskin`.

This fixes it.

<details>
  <summary>Previous implementation for posterity</summary>

Back from my short code break, time to fix some of the things I've been
annoyed by.

Firstly, I noticed pride pins could no longer be reskinned since the
alt-click refactor.
Looking into it, this seems to be because we now only register this on
`Initialize(...)` if `unique_reskin` has been set:

https://github.com/tgstation/tgstation/blob/9145ecb7e1e44635a1056fc704adfa3d764325e6/code/game/objects/items.dm#L267-L269
While due to using a global list we don't set this in the item
definition, but in `Initialize(...)` :

https://github.com/tgstation/tgstation/blob/9145ecb7e1e44635a1056fc704adfa3d764325e6/code/modules/clothing/under/accessories/badges.dm#L196-L198
Where we call the parent proc _before_ setting `unique_reskin`, and thus
not registering our ability to reskin.

So all we do is set this to our global list _before_ we call the parent
proc.
```dm
/obj/item/clothing/accessory/pride/Initialize(mapload)
	unique_reskin = GLOB.pride_pin_reskins // Set before parent proc checks for it.
	. = ..()
```
This fixes it.

</details>

## Why It's Good For The Game

Fixes pride pin reskinning.
Theoretically makes it easier to avoid this happening in the future, and
allows `setup_reskinning()` to be manually called in the case of values
being edited post-initialize.

<details>
  <summary>Previous pitch for posterity</summary>

Fixes pride pin reskinning.

</details>

## Changelog
🆑
fix: Pride pins can be reskinned again with alt-click.
/🆑

code/game/objects/items.dm

@@ -268,9 +268,7 @@
 	if(LAZYLEN(embedding))
 		updateEmbedding()
 
-	if(unique_reskin)
-		RegisterSignal(src, COMSIG_CLICK_ALT, PROC_REF(on_click_alt_reskin))
-		register_context()
+	setup_reskinning()
 
 
 /obj/item/Destroy(force)

code/game/objects/items_reskin.dm

@@ -11,12 +11,41 @@
 	INVOKE_ASYNC(src, PROC_REF(reskin_obj), user)
 	return CLICK_ACTION_SUCCESS
 
+/**
+ * Checks if we should set up reskinning,
+ * by default if unique_reskin is set.
+ *
+ * Called on setup_reskinning().
+ * Inheritors should override this to add their own checks.
+ */
+/obj/item/proc/check_setup_reskinning()
+	SHOULD_CALL_PARENT(TRUE)
+	if(unique_reskin)
+		return TRUE
+
+	return FALSE
+
+/**
+ * Registers signals and context for reskinning,
+ * if check_setup_reskinning() passes.
+ *
+ * Called on Initialize(...).
+ * Inheritors should override this to add their own setup steps,
+ * or to avoid double calling register_context().
+ */
+/obj/item/proc/setup_reskinning()
+	SHOULD_CALL_PARENT(FALSE)
+	if(!check_setup_reskinning())
+		return
+
+	RegisterSignal(src, COMSIG_CLICK_ALT, PROC_REF(on_click_alt_reskin))
+	register_context()
 
 /**
  * Reskins object based on a user's choice
  *
  * Arguments:
- * * M The mob choosing a reskin option
+ * * user The mob choosing a reskin option
  */
 /obj/item/proc/reskin_obj(mob/user)
 	if(!LAZYLEN(unique_reskin))

code/modules/clothing/under/_under.dm

@@ -51,10 +51,15 @@
 	if(random_sensor)
 		//make the sensor mode favor higher levels, except coords.
 		sensor_mode = pick(SENSOR_VITALS, SENSOR_VITALS, SENSOR_VITALS, SENSOR_LIVING, SENSOR_LIVING, SENSOR_COORDS, SENSOR_COORDS, SENSOR_OFF)
-	if(!unique_reskin) // Already registered via unique reskin
-		register_context()
+	register_context()
 	AddElement(/datum/element/update_icon_updates_onmob, flags = ITEM_SLOT_ICLOTHING|ITEM_SLOT_OCLOTHING, body = TRUE)
 
+/obj/item/clothing/under/setup_reskinning()
+	if(!check_setup_reskinning())
+		return
+
+	// We already register context in Initialize.
+	RegisterSignal(src, COMSIG_CLICK_ALT, PROC_REF(on_click_alt_reskin))
 
 /obj/item/clothing/under/add_context(atom/source, list/context, obj/item/held_item, mob/living/user)
 	. = ..()

code/modules/clothing/under/accessories/_accessories.dm

@@ -30,6 +30,13 @@
 	. = ..()
 	register_context()
 
+/obj/item/clothing/accessory/setup_reskinning()
+	if(!check_setup_reskinning())
+		return
+
+	// We already register context regardless in Initialize.
+	RegisterSignal(src, COMSIG_CLICK_ALT, PROC_REF(on_click_alt_reskin))
+
 /**
  * Can we be attached to the passed clothing article?
  */

code/modules/clothing/under/accessories/badges.dm

@@ -195,9 +195,13 @@ GLOBAL_LIST_INIT(pride_pin_reskins, list(
 	icon_state = "pride"
 	obj_flags = UNIQUE_RENAME | INFINITE_RESKIN
 
-/obj/item/clothing/accessory/pride/Initialize(mapload)
-	. = ..()
+/obj/item/clothing/accessory/pride/setup_reskinning()
 	unique_reskin = GLOB.pride_pin_reskins
+	if(!check_setup_reskinning())
+		return
+
+	// We already register context regardless in Initialize.
+	RegisterSignal(src, COMSIG_CLICK_ALT, PROC_REF(on_click_alt_reskin))
 
 /obj/item/clothing/accessory/deaf_pin
 	name = "deaf personnel pin"