Digitigrade code refactor and shoes + explorer suit (Using GAGS and zero sprite bloat) (#88096)

## About The Pull Request
Refactors and extends the existing [digitigrade clothing
system](https://github.com/tgstation/tgstation/pull/85406) to also
support oversuits and shoes (only enabled for sneakers, specific boots,
and shaft miner's explorer suit). All digitigrade-specific clothes are
generated by GAGS by color sampling the base sprite and applying it to a
greyscale template.


![image](https://github.com/user-attachments/assets/c4ce5996-9373-4d76-a0e5-a6b094dd10b4)

More up to date boots:

![image](https://github.com/user-attachments/assets/8ead8056-25a3-42dd-9fde-e838e2a810b9)


![image](https://github.com/user-attachments/assets/783a1201-8a77-45a0-af85-8a63b41b63a8)


Credit to MrMelbert for prototype code and Junkgle for new sprites

## Why It's Good For The Game
Looks good, doesn't introduce maintainability issues or sprite bloat

## Changelog
🆑
add: digitigrade lizards can wear certain shoes and suits
image: added digitigrade shoes & oversuit templates
refactor: improved digi clothing generator code
/🆑

---------

Co-authored-by: MrMelbert <kmelbert4@gmail.com>
Co-authored-by: Roryl-c <5150427+Roryl-c@users.noreply.github.com>

code/modules/mining/equipment/explorer_gear.dm

@@ -6,6 +6,7 @@
 	icon = 'icons/obj/clothing/suits/utility.dmi'
 	worn_icon = 'icons/mob/clothing/suits/utility.dmi'
 	inhand_icon_state = null
+	supports_variations_flags = CLOTHING_DIGITIGRADE_MASK
 	body_parts_covered = CHEST|GROIN|LEGS|ARMS
 	cold_protection = CHEST|GROIN|LEGS|ARMS
 	min_cold_protection_temperature = FIRE_SUIT_MIN_TEMP_PROTECT
@@ -15,6 +16,9 @@
 	armor_type = /datum/armor/hooded_explorer
 	resistance_flags = FIRE_PROOF
 
+/obj/item/clothing/suit/hooded/explorer/get_general_color(icon/base_icon)
+	return "#796755"
+
 /datum/armor/hooded_explorer
 	melee = 30
 	bullet = 10