Fix recording truncation and rate mismatch causing static

The recording pipeline had two bugs that combined to produce
buzzing/static in recorded audio:

1. NormalizeStereoFrame truncated incoming audio frames to
   frameSize*AudioChannels samples. When the Opus decoder produced
   20ms frames (1920 stereo samples) but the recorder used a 10ms
   frameSize (960 samples), half the audio from every packet was
   silently dropped.

2. The recorder's run() loop dequeued one fixed-length frame per
   source per tick. After truncation, the remaining 10ms of each
   20ms packet was gone, so every other tick produced silence.
   This 50 Hz on/off pattern sounded like static.

Fixes:
- NormalizeStereoFrame no longer truncates; it only converts mono
  to stereo and preserves all audio data
- RecordAudioFrame now accepts an explicit stereo flag from callers
  instead of guessing from sample count (which failed for even-length
  mono data like 480-sample mic frames)
- run() accumulates variable-length frames per source and consumes
  them in fixed-size chunks, preserving any leftover for the next tick

gumble/gumbleopenal/stream.go

@@ -45,7 +45,7 @@ type FilePlayer interface {
 }
 
 type Recorder interface {
-	RecordAudioFrame(source uint32, samples []int16)
+	RecordAudioFrame(source uint32, samples []int16, stereo bool)
 }
 
 const recorderOutgoingSource uint32 = ^uint32(0)
@@ -742,7 +742,7 @@ func (s *Stream) processAudioPacket(packet *gumble.AudioPacket, user *gumble.Use
 		}
 	}
 	if recorder != nil && recordPtr > 0 {
-		recorder.RecordAudioFrame(user.Session, recordBuffer[:recordPtr])
+		recorder.RecordAudioFrame(user.Session, recordBuffer[:recordPtr], true)
 	}
 
 	if len(emptyBufs) == 0 {
@@ -932,7 +932,7 @@ func (s *Stream) sourceRoutine(inputDevice *string, stop chan bool, done chan st
 				// Send stereo buffer when file is playing
 				outgoing <- gumble.AudioBuffer(outputBuffer)
 				if recorder := s.getRecorder(); recorder != nil {
-					recorder.RecordAudioFrame(recorderOutgoingSource, outputBuffer)
+					recorder.RecordAudioFrame(recorderOutgoingSource, outputBuffer, true)
 				}
 			} else if hasMicInput {
 				// Send mic when no file is playing. If the microphone is
@@ -949,7 +949,7 @@ func (s *Stream) sourceRoutine(inputDevice *string, stop chan bool, done chan st
 				}
 				outgoing <- gumble.AudioBuffer(outBuf)
 				if recorder := s.getRecorder(); recorder != nil {
-					recorder.RecordAudioFrame(recorderOutgoingSource, outBuf)
+					recorder.RecordAudioFrame(recorderOutgoingSource, outBuf, false)
 				}
 			}
 		}