Expose internal device properties negotiated by the audio backend

After initialization, miniaudio's ma_device struct contains both the
requested and the actual (internal) format, channel count, and sample
rate for capture and playback. The internal values reflect what the
audio backend actually negotiated, which can differ from what the
application requested.

A common case is ALSA's dsnoop plugin, which locks the hardware at a
fixed sample rate and silently resamples. The existing SampleRate()
method returns the requested rate, hiding the mismatch. The new
CaptureInternalSampleRate() and PlaybackInternalSampleRate() methods
let callers detect this.

New methods:
  - CaptureInternalSampleRate / PlaybackInternalSampleRate
  - CaptureInternalFormat / PlaybackInternalFormat
  - CaptureInternalChannels / PlaybackInternalChannels

Author: tphakala

device.go

@@ -101,6 +101,46 @@ func (dev *Device) SampleRate() uint32 {
 	return uint32(dev.cptr().sampleRate)
 }
 
+// CaptureInternalSampleRate returns the sample rate negotiated with the audio
+// backend for capture. This may differ from SampleRate() when the backend
+// cannot honor the requested rate, for example when ALSA's dsnoop plugin locks
+// the hardware at a fixed rate and resamples in software.
+func (dev *Device) CaptureInternalSampleRate() uint32 {
+	return uint32(dev.cptr().capture.internalSampleRate)
+}
+
+// PlaybackInternalSampleRate returns the sample rate negotiated with the audio
+// backend for playback.
+func (dev *Device) PlaybackInternalSampleRate() uint32 {
+	return uint32(dev.cptr().playback.internalSampleRate)
+}
+
+// CaptureInternalFormat returns the sample format negotiated with the audio
+// backend for capture. This may differ from CaptureFormat() when the backend
+// performs format conversion internally.
+func (dev *Device) CaptureInternalFormat() FormatType {
+	return FormatType(dev.cptr().capture.internalFormat)
+}
+
+// PlaybackInternalFormat returns the sample format negotiated with the audio
+// backend for playback.
+func (dev *Device) PlaybackInternalFormat() FormatType {
+	return FormatType(dev.cptr().playback.internalFormat)
+}
+
+// CaptureInternalChannels returns the channel count negotiated with the audio
+// backend for capture. This may differ from CaptureChannels() when the backend
+// performs channel conversion internally.
+func (dev *Device) CaptureInternalChannels() uint32 {
+	return uint32(dev.cptr().capture.internalChannels)
+}
+
+// PlaybackInternalChannels returns the channel count negotiated with the audio
+// backend for playback.
+func (dev *Device) PlaybackInternalChannels() uint32 {
+	return uint32(dev.cptr().playback.internalChannels)
+}
+
 // Start activates the device.
 // For playback devices this begins playback. For capture devices it begins recording.
 //