Fix iOS first recording returning null due to premature session termination

[Copilot]

On iOS, StopAsync() returns null on the first recording but works correctly on subsequent recordings. Android is unaffected.

Root Cause

The AudioRecorder constructor calls FinishSession() before any session is initialized, leaving the AVAudioSession in an inconsistent state for the first recording.

Changes

Session lifecycle

• Remove premature FinishSession() call from constructor
• Session now properly initialized on first StartAsync() without prior deactivation

Resource management

• Extract cleanup logic into CleanupRecorderResources() to handle disposal consistently
• Dispose previous recorder instances in StartAsync() before creating new ones
• Reset all fields (recorder, destinationFilePath, finishedRecordingCompletionSource) after StopAsync() completes

Event handling

• Unsubscribe from FinishedRecording event before disposal
• Parameterize cleanup method to avoid redundant unsubscriptions

// Before: Constructor interfered with first recording
public AudioRecorder(AudioRecorderOptions options)
{
    this.audioRecorderOptions = options;
    ActiveSessionHelper.FinishSession(options);  // ❌ Premature
}

// After: Clean initialization
public AudioRecorder(AudioRecorderOptions options)
{
    this.audioRecorderOptions = options;
}

Impact

First recording on iOS now works correctly, matching Android behavior. No changes to other platforms.

Original prompt

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This section details on the original issue you should resolve

<issue_title>iOS returns a null IAudioSource object after the first recording, subsequent recordings are OK, Android OK</issue_title>
<issue_description>StopAsync() works as expected with Android, but on IOS, the first recording StopAsync() returns a null object. Subsequent recordings return a usable IAudioSource object. I've tried the Plugin.Maui.Audio.Sample and I don't see any issues with it, so it points to my code, but I do not see any problems with it.
While recording, I am able to poll audioRecorder.IsRecording and see that it is true.
Under what circumstances does StopAsync() return null? See vStopRecord() below.

I have the following methods to start/stop recording:

public async Task vStartRecord() {
       if ( await CheckPermissionIsGrantedAsync<Microphone>() ) {
           audioRecorder = audioManager.CreateRecorder();
           if ( audioRecorder == null ) {
               var toast = Toast.Make("error creating audio recorder", CommunityToolkit.Maui.Core.ToastDuration.Long, 12);
               await toast.Show();
               return;
               }
           var toast2 = Toast.Make("audio recorder can record: " + audioRecorder.CanRecordAudio, CommunityToolkit.Maui.Core.ToastDuration.Long, 12);
           await toast2.Show();

           var options = new AudioRecorderOptions {
               Channels = ChannelType.Mono,
               BitDepth = BitDepth.Pcm16bit,
               Encoding = Plugin.Maui.Audio.Encoding.Wav,
               SampleRate = 8000,
               ThrowIfNotSupported = true,
               #if IOS || MACCATALYST
               Category = AVFoundation.AVAudioSessionCategory.PlayAndRecord
               #endif
               };

           try {
               await audioRecorder.StartAsync(options);
               }

           catch {
               var toast = Toast.Make("error starting audio recorder", CommunityToolkit.Maui.Core.ToastDuration.Long, 12);
               await toast.Show();
               return;
               }
           }
      
       else {
           var toast = Toast.Make("no permission to record", CommunityToolkit.Maui.Core.ToastDuration.Long, 12);
           await toast.Show();
           }
       }

   public async Task vStopRecord() {
       if ( audioRecorder != null ) {
           audioSource = await audioRecorder.StopAsync();
           if ( audioSource != null ) {
               var toast = Toast.Make("no audio recorded", CommunityToolkit.Maui.Core.ToastDuration.Long, 12);
               await toast.Show();
               }
           }
       }

```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes iOS returns a null IAudioSource object after the first recording, subsequent recordings are OK, Android OK #187

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Pull Request Overview

This PR fixes a bug where the first audio recording on iOS returns null from StopAsync() while subsequent recordings work correctly. The root cause was a premature FinishSession() call in the constructor that left the AVAudioSession in an inconsistent state before the first recording started.

Key changes:

• Removed premature FinishSession() call from the AudioRecorder constructor
• Added CleanupRecorderResources() method to properly manage recorder lifecycle and prevent resource leaks
• Implemented cleanup of previous recorder instances in StartAsync() and after StopAsync() completes

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[jfversluis]

Issue reporter resolved their issue so this one can be closed for now.