Phase 4: Implement MediaStreamTrack constraint methods

[General-Fault]

Implement MediaStreamTrack::GetCapabilities() → MediaTrackCapabilities, GetSettings() → MediaTrackSettings, ApplyConstraints(MediaTrackConstraints). Ensure marshalling round-tripping works correctly.

Dependencies: Phase 2

Files to modify:

• WebRtcInterop/Media/MediaStreamTrack.h/cpp

[General-Fault]

Status update from merged PR #57 (#57):

Implemented in this phase:

• MediaStreamTrack::ApplyConstraints(...) no longer throws for baseline usage.
• Applied constraints are now persisted on the wrapper and returned by GetConstraints().

Still pending for this issue (full scope):

• GetCapabilities() currently returns default/empty capability object.
• GetSettings() currently returns default/empty settings object.
• ApplyConstraints(...) is not yet applied to native track configuration (no native capability/settings round-trip yet).

Plan update:

1. Wire native capability/settings extraction and marshal to managed MediaTrackCapabilities / MediaTrackSettings.
2. Apply supported constraints to native tracks and surface unsupported/unsatisfied cases explicitly.
3. Add interop tests for capability/settings fidelity and constraint application behavior.