Improve source helper test coverage

[kemsta]

No description provided.

[Copilot]

Pull request overview

This PR factors common ScreenCaptureKit helper logic (item selection and audio buffer normalization) into a shared internal module and adds unit tests to improve coverage across the source implementations.

Changes:

• Add sources::screen_capture with shared helpers for selecting items by id(s) and normalizing audio buffers, including dedicated unit tests.
• Refactor app_audio and system_audio to use the shared helpers and add unit tests for display/application selection behavior.
• Extract microphone config validation into a helper and add a focused test; adjust cli_tester logging/stats printing.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
core_engine/src/sources/system_audio.rs	Uses shared selection/audio normalization helpers; adds selection tests.
core_engine/src/sources/screen_capture.rs	New internal helper module with selection + normalization logic and tests.
core_engine/src/sources/mod.rs	Registers the new internal screen_capture module.
core_engine/src/sources/microphone.rs	Extracts config validation into helper + adds a test.
core_engine/src/sources/app_audio.rs	Uses shared selection/audio normalization helpers; adds selection tests.
cli_tester/src/main.rs	Adds extra case-flow prints; updates stats field access (currently incorrect).

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

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