Implement duplex mode API for ALSA

[SolarLiner]

Description

Implements the duplex mode API and for ALSA.

Needs #31 .

Closes #30.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code cleanup or refactor

How Has This Been Tested?

Ran the loopback example.

Checklist:

• My code follows the style guidelines of this project
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Wherever possible, I have added tests that prove my fix is effective or that my feature works. For changes that need to be validated manually (i.e. a new audio driver), use examples that can be run to easily validate them.
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

[SolarLiner]

@geom3trik if you're okay with this, I think I'll merge this into the Duplex API PR to make it easier to handle those changes