refactor: extract shared player.ID type and GenerateID to player package

Both game and snake packages had identical PlayerID types and the snake
package imported game.GenerateID. Now both use player.ID and
player.GenerateID from the shared player package.

snake/store.go

@@ -5,7 +5,7 @@ import (
 	"sync"
 
 	"github.com/ryanhamamura/c4/db/repository"
-	"github.com/ryanhamamura/c4/game"
+	"github.com/ryanhamamura/c4/player"
 )
 
 type SnakeStore struct {
@@ -38,7 +38,7 @@ func (ss *SnakeStore) Create(width, height int, mode GameMode, speed int) *Snake
 	if speed <= 0 {
 		speed = DefaultSpeed
 	}
-	id := game.GenerateID(4)
+	id := player.GenerateID(4)
 	sg := &SnakeGame{
 		ID: id,
 		State: &GameState{
@@ -172,7 +172,7 @@ func (si *SnakeGameInstance) GetGame() *SnakeGame {
 	return si.game.snapshot()
 }
 
-func (si *SnakeGameInstance) GetPlayerSlot(pid PlayerID) int {
+func (si *SnakeGameInstance) GetPlayerSlot(pid player.ID) int {
 	si.gameMu.RLock()
 	defer si.gameMu.RUnlock()
 	for i, p := range si.game.Players {