move player id to a separate package

Later, this package could hold stuff like MMR. It's just a type for now.

game/player.go

@@ -1,13 +1,13 @@
 package game
 
-import "slices"
+import (
+	"slices"
 
-// PlayerID is a unique ID for a player.
+	"git.sunturtle.xyz/studio/shotgun/player"
-// May just be IPv6 (or IPv4-in-6) of their connection, or a UUID.
+)
-type PlayerID [16]byte
 
 type Player struct {
-	ID    PlayerID
+	ID    player.ID
 	HP    int8
 	Items [8]Item
 	Cuffs CuffState

player/player.go

@@ -0,0 +1,6 @@
+// Package player implements data about players outside games.
+package player
+
+// ID is a unique ID for a player.
+// May just be IPv6 (or IPv4-in-6) of their connection, or a UUID.
+type ID [16]byte