TGUI list conversions + bug fixes (#63354)

About The Pull Request

    Converts more inputs to TGUI. Possibly all user-facing input lists in the game.
    Did any surrounding text/number inputs as well
    Added null choice support so users can press cancel.
    Added some misc TGUI input fixes
    Fixed custom vendors while I was there

I refactored a lot of code while just poking around.
Primarily, usage of .len in files where I was already working on lists.
Some code was just awful - look at guardian.dm and its non use of early returns
If there are any disputes, I can revert it just fine, those changes are not integral to the PR.
Why It's Good For The Game

Fixes #63629
Fixes #63307
Fixes custom vendors /again/
Text input is more performant.
Part of a long series of TGUI conversion to make the game more visually appealing
Changelog

cl
refactor: The majority of user facing input lists have been converted to TGUI.
refactor: Tgui text inputs now scale with entered input.
fix: Many inputs now properly accept cancelling out of the menu.
fix: Fixes an edge case where users could not press enter on number inputs.
fix: Custom vendor bluescreen.
fix: You can now press ENTER on text inputs without an entry to cancel.
/cl

code/modules/admin/verbs/SDQL2/SDQL_spells/spell_edit_menu.dm

@@ -322,13 +322,14 @@ GLOBAL_LIST_INIT_TYPED(sdql_spells, /obj/effect/proc_holder/spell, list())
 			saved_vars[params["name"]] = !saved_vars[params["name"]]
 		if("path_variable")
 			var/new_path = tgui_input_list(user, "Select type.", "Add SDQL Spell", typesof(text2path(params["root_path"])))
-			if(new_path)
-				saved_vars[params["name"]] = new_path
-				var/datum/sample = new new_path
-				var/list/overrides = list_vars[special_var_lists[params["name"]]]
-				overrides = overrides&sample.vars
-				qdel(sample)
-				icon_needs_updating(params["name"])
+			if(isnull(new_path))
+				return
+			saved_vars[params["name"]] = new_path
+			var/datum/sample = new new_path
+			var/list/overrides = list_vars[special_var_lists[params["name"]]]
+			overrides = overrides&sample.vars
+			qdel(sample)
+			icon_needs_updating(params["name"])
 		if("list_variable_add")
 			if(!list_vars[params["list"]])
 				list_vars[params["list"]] = list()