Audio server utils module (New) (#2131)

* Add audio server utilities module

Introduces a unified interface for working with PulseAudio and PipeWire
audio servers without requiring deep knowledge of either system.

Features:
- AudioServerUtils factory that auto-detects the running audio server
- PipewireUtils: Full support for PipeWire's device/profile/node hierarchy
- PulseaudioUtils: Support for PulseAudio sink/source management
- Node abstraction representing audio sinks and sources
- Methods to list, iterate, set default, and control volume of audio nodes
- CLI interface for listing and interactively selecting audio nodes

The iterator pattern (iter_sinks/iter_sources) automatically activates
profiles before yielding nodes, making them immediately usable.

* Add tests for audio server utilities

Comprehensive test coverage for the audio_server_utils module:

- NodeTests: Basic Node class instantiation
- AudioServerUtilsTests: Factory pattern and server detection
- PipewireUtilsTests: PipeWire-specific functionality including
  pw-dump parsing, device/profile/node handling, and volume control
- PulseaudioUtilsTests: PulseAudio-specific functionality including
  pactl parsing, sink/source management, and volume control

Signed-off-by: Paolo Gentili <paolo.gentili@canonical.com>

* Use universal_newlines in subprocess.check_output

Signed-off-by: Paolo Gentili <paolo.gentili@canonical.com>

* Add more parser tests with textwrap.dedent

Signed-off-by: Paolo Gentili <paolo.gentili@canonical.com>

* Add end-to-end integration tests for audio utilities

Signed-off-by: Paolo Gentili <paolo.gentili@canonical.com>

* fix: format

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Signed-off-by: Paolo Gentili <paolo.gentili@canonical.com>

Author: p-gentili