- Add is_underwater() and set_underwater() to ClientPlayer.
- Change get_world() to return non-const reference for audio access.
- Update Camera::update_move_camera() to detect water block changes and trigger transition sound.
- Add repeating timer in ClientWorld to play random bubble ambient sounds while underwater.
- Include new ambient sound assets for water transitions and bubbles.
- Also add sand walk sound asset (unused in this commit).
Add four ocean wave FLAC sound files and play one randomly when player is within 10 blocks of sea level and in an ocean biome. Include a Random member initialized from ChunkGenerator seed for consistent randomization.
Add a new `Timer` class that operates in seconds (using `TimeType`) alongside the existing `TickTimer` which uses `TickType`. Rename the original `Timer` to `TickTimer` throughout the codebase. Update `ClientWorld` to maintain separate maps for tick-based and time-based timers, and replace the hardcoded footstep timer in `ClientPlayer` with a time-based callback timer. Also add `play_2d` to `AudioEngine` and load an ambient bird sound to demonstrate the new timer functionality.
