Add dynamic rootless processing and USB output rates

[legendcodermartino1245]

Draft / dependency

This is stacked on and depends on #337. Until that PR merges, GitHub shows both commits here. The dynamic rootless-rate work is the second commit (03cbbba).

Summary

Allow rootless processing to follow active source or physical USB hardware sample rates instead of clamping processing to 44.1/48 kHz.

Adds two USB modes:

• Follow USB hardware rate: rebuild processing at the physical output rate.
• Follow source rate: process at the source rate and allow Android to perform final conversion.

Implementation

• detects active playback source rates
• tracks route changes and rebuilds AudioRecord/AudioTrack as needed
• uses Android 14 preferred mixer attributes where available
• exposes source, processing, and hardware rates separately
• supports processing rates through 384 kHz
• preserves safe fallbacks when detection fails

Platform caveats

Some rate discovery relies on hidden playback configuration fields and AudioFlinger diagnostic output because rootless Android does not expose the complete physical path through a stable public API. This is why the PR is opened as a draft for design feedback.

Testing

• all 16 rootless F-Droid unit tests pass
• rootless debug APK builds successfully
• tested on a Samsung device with a FiiO BTR7 USB DAC
• verified a 96 kHz JamesDSP processing path, 96 kHz Android A2DP output, and LDAC negotiated at 96 kHz/24-bit

[timschneeb]

Looks good 👍 I'll merge it when you mark the PR as ready

Some rate discovery relies on hidden playback configuration fields and AudioFlinger diagnostic output because rootless >Android does not expose the complete physical path through a stable public API. This is why the PR is opened as a draft for >design feedback.

Using hidden APIs is fine, the app already does that pretty heavily anyways.