Fix start local audio

[hiroshihorie]

Ensure native ADM is started when track.start() is called so audio frames get generated (for visualizer)
Also expose manual adm start/stop methods.

[bdlukaa]

@hiroshihorie when disposing the local track, the system says the audio is still being captured.

I feel like stopLocalRecording isn't being called on stop() or dispose().

[bdlukaa]

I've been using this branch for a while.

iOS only.
I got this bug:

String: Unable to start local recording: Error: adm api failed with code: -1
#0      NativeAudioManagement.startLocalRecording (package:flutter_webrtc/src/native/audio_management.dart:79)
  File "<asynchronous suspension>"
#2      LocalAudioTrack.start (package:livekit_client/src/track/local/audio.dart:119)
  File "<asynchronous suspension>"
#4      _PreJoinScreenState._initializeLocalAudio (package:totem_app/features/sessions/screens/pre_join_screen.dart:223)
  File "<asynchronous suspension>"
#6      Future.wait.<fn> (dart:async/future.dart:546)
  File "<asynchronous suspension>"
#8      _PreJoinScreenState._initializeAndCheckPermissions.<fn> (package:totem_app/features/sessions/screens/pre_join_screen.dart:163)

[hiroshihorie]

Closing this one, it has been superseded by #1115 (shipped in 2.9.0).

That PR moved audio processing setup into the capture start path, so track.start() now starts the native ADM through the SDK's own channel even when the track is not published. The visualizer use case this PR was for works on 2.9.0+ with a plain track.start(), no manual ADM calls needed.

@bdlukaa the two issues you reported here are also addressed by the new path: failures now surface as typed AudioProcessingException with a reason instead of the opaque adm error string, and tracks clean up capture when startup fails. If you still hit either on 2.9.0+ please open an issue.

The one part of this PR that did not land anywhere is the public Hardware.startLocalRecording/stopLocalRecording API. Will open a separate PR with @experimental annotations if a concrete use case for manual ADM control comes up.