Optimize /atom/movable/Initialize with faster check for blocks_emissive [140ms on init] (#74453)

Quoting the comment:

This one is incredible.
`if (x) else { /* code */ }` is surprisingly fast, and it's faster than
a switch, which is seemingly not a jump table.
From what I can tell, a switch case checks every single branch
individually, although sane, is slow in a hot proc like this.
So, we make the most common `blocks_emissive` value,
EMISSIVE_BLOCK_GENERIC, 0, getting to the fast else branch quickly.
If it fails, then we can check over every value it can be (here,
EMISSIVE_BLOCK_UNIQUE is the only one that matters).
This saves several hundred milliseconds of init time.

code/controllers/admin.dm

@@ -1,7 +1,7 @@
 // Clickable stat() button.
 /obj/effect/statclick
 	name = "Initializing..."
-	blocks_emissive = NONE
+	blocks_emissive = EMISSIVE_BLOCK_NONE
 	var/target
 
 INITIALIZE_IMMEDIATE(/obj/effect/statclick)