Respect per-player action specs in ActionReader

[sylvesterkaczmarek]

Summary

Make the human-player ActionReader respect the action names actually available to each player.

The current implementation collects action names globally across the full DMLab2D action spec. When player action specs are asymmetric, selecting one player can therefore add action keys that do not exist for that player.

This change:

• records action names per player prefix
• reads only actions supported by the currently selected player
• continues emitting zero values for the other valid action-spec keys
• preserves existing behavior for symmetric player action specs
• adds focused regression coverage

Testing

Added tests with asymmetric player action specs verifying that each selected player produces only its own valid action keys.