Always treat waveform as List<Float> (#1663)

[MSC3246](https://github.com/matrix-org/matrix-spec-proposals/pull/3246) specifies the waveform as a list of ints because:

> Because floating point numbers are not allowed in Matrix events

Though DSP on audio data is almost always done using their floating point representation.
This PR brings the float<->int rescaling in the `matrix` module so that the application code can always work with float waveform samples.

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/room/FakeMatrixRoom.kt

@@ -387,7 +387,7 @@ class FakeMatrixRoom(
     override suspend fun sendVoiceMessage(
         file: File,
         audioInfo: AudioInfo,
-        waveform: List<Int>,
+        waveform: List<Float>,
         progressCallback: ProgressCallback?
     ): Result<MediaUploadHandler> = fakeSendMedia(progressCallback)