Unit tests radio, saymode, and language prefix keys (#71328)

## About The Pull Request
This PR unit tests radio/saymode prefixes together, and language
prefixes on their own, for any possible overlaps and duplicates

Moved mafia saymode key to :1 and holopad key to :2, we're running out
of radio keys and i'm too afraid to move to 2-letter

## Why It's Good For The Game
1. Unit tests are good
2. https://github.com/tgstation/tgstation/pull/71326 this is bad

🆑 
spellcheck: Mafia changeling say prefix is now :1, and holopad say is
now :2
/🆑

Co-authored-by: Zephyr <12817816+ZephyrTFA@users.noreply.github.com>

code/datums/saymode.dm

@@ -87,7 +87,7 @@
 
 
 /datum/saymode/holopad
-	key = "h"
+	key = "2"
 	mode = MODE_HOLOPAD
 
 /datum/saymode/holopad/handle_message(mob/living/user, message, datum/language/language)
@@ -98,7 +98,7 @@
 	return TRUE
 
 /datum/saymode/mafia
-	key = "j"
+	key = "1"
 	mode = MODE_MAFIA
 
 /datum/saymode/mafia/handle_message(mob/living/user, message, datum/language/language)