Add volume and mute controls

[contemno]

Add volume and mute controls

This PR adds support for controlling monitor audio volume and mute state.

Changes

New VCP Codes

• Added sound_volume (0x62) - continuous value for audio volume control
• Added display_audio_mute_mode (0x8D) - non-continuous value for mute state

New API

• Added AudioMuteMode enum with on and off states
• Added Monitor.get_volume() / Monitor.set_volume() methods
• Added Monitor.get_audio_mute_mode() / Monitor.set_audio_mute_mode() methods

CLI Changes

New command-line arguments:

• --get-volume - Get the volume of the first monitor
• --set-volume <value> - Set the volume of all monitors (0-100)
• --get-audio-mute-mode - Get the audio mute mode of the first monitor
• --set-audio-mute-mode <on|off> - Set the audio mute mode of all monitors

Testing

• Added unit tests for volume get/set operations
• Added unit tests for audio mute mode get/set with various input types
• Added CLI tests for all new arguments

Usage Examples

from monitorcontrol import get_monitors

for monitor in get_monitors():
  with monitor:
    try:
      # Volume control
      monitor.set_volume(75)
      print(f"Current volume: {monitor.get_volume()}")
    except:
      print("Volume control unsupported by monitor")
    try:            
      # Mute control
      monitor.set_audio_mute_mode("on")
      print(f"Mute state: {monitor.get_audio_mute_mode()}")
    except:
      print("Mute control unsupported by monitor")

# CLI usage
python -m monitorcontrol --set-volume 50
python -m monitorcontrol --get-volume
python -m monitorcontrol --set-audio-mute-mode on
python -m monitorcontrol --get-audio-mute-mode