v3 release

[sotetsuk]

• Staging auto_reset as option #1263
• Use NamedTuple instead of dataclass #1192
• Remove player_id argument in Env.observe #1154
• src layout src/pgx/...
• (almost) single file implementations [Internal change] Decompose the game logic and API #1127
• defer observation/legal_action_mask computation?
• mlx/torch ports for some game?