[FEAT] Add unit and integration tets and enable testability for core components

[luthfiampas]

Requirements

• I have searched the existing issues to ensure this feature has not already been requested.
• I have clearly described the problem and the proposed solution.
• I have considered alternative solutions.

1. Is your feature request related to a problem? Please describe.

I noticed that it currently lacks unit tests, which makes it a bit challenging to confidently extend, refactor, or verify the behavior of core components.

2. Describe the Solution You'd Like

It would be wonderful to have some foundational unit tests in place for key components, even if minimal, to establish a baseline. The main goal is to test critical components and make the architecture more testable if necessary. I am happy to help by submitting initial tests for review when I have time :)

3. Describe Alternatives You've Considered

I considered writing only integration tests by running a sample app and observing behavior, but these tests are slower and don't easily catch small logic bugs or regressions.

4. Proposed API (if applicable)

No new public API needed. Suggest adding SoundFlow.UnitTests and SoundFlow.IntegrationTests projects. Minor internal refactoring to support DI and mocking as needed.

5. Benefits

Improves code quality, eases contributions, and reduces bugs. It also might helps ensure robust handling of edge cases in audio processing.

6. Potential Drawbacks/Challenges

• Some effort may be needed to make parts of the code more testable.
• Testing audio processing can be complex and may require mocks or utilities for verifying stream content.
• Maintaining tests does introduce some overhead, though the long-term benefits usually outweigh this.

7. Additional Context

Projects like NAudio offer some inspiration in terms of structure and testability. I’d love to see SoundFlow take a similar path, even with a modest starting point for tests.

[LSXPrime]

Unlike most of my projects, SoundFlow was released without unit tests. It felt simple and straightforward at the time, and any bugs or unexpected behaviors weren't a significant issue. My original plan was simply to build and archive it, having no personal use case, especially after I dismissed the one application it was intended for.

However, as SoundFlow unexpectedly gained traction, I began to deeply regret not implementing tests before subsequent refactoring or extensions. The challenge now is critical, I have less than two months before starting mandatory military service, during which I'll be completely cut off from technology for ~1.5y (where I will even forget how a mobile phone looks).

This tight deadline means I lack the time to write any tests, while still needing to tackle several open bugs and crucial feature requests.

I will add this to the backlog as a feature request for now, to be addressed upon my return.