Add clientbound packets: ChangeDifficulty, SetDefaultSpawnPosition, SetExperience

[OmarAfet]

• Add CChangeDifficulty clientbound packet
  Informs the client of the current difficulty level and lock state.
• Add CSetDefaultSpawnPosition clientbound packet
  Sets the player's compass target and default respawn position with dimension, coordinates, and angles.
• Add CSetExperience clientbound packet
  Sends the player's experience bar progress, level, and total points.

[Joniii11]

difficulty packet is implemented here #108

[4lve]

Thanks for your PR but we only accept PRs than include code changes and not just packets. Feel free to join the discord and discuss though!