The default Stream implementation of this method has to rent an array so it can call the overload that accepts an array, and then copy the output over. This is because the array overload is required and the span overload was only added more recently.
We can avoid the overhead of this by implementing the span overload and working with the destination span directly. Do so for all classes we have that derive from Stream, and redirect their array overload to the span overload for code reuse.
The Stream.ReadByte method is implemented by allocating a 1 byte buffer and calling into Read(byte[], int, int). Override ReadByte in derived classes to avoid needing to allocate this small temp buffer.
Also, fix some bugs in the stream implementations. Remove Write capability from MergedStream that didn't make sense. Add guards into SegmentStream to ensure reads and writes belonged to the segment - otherwise a reader or writer could access regions of the base stream that were outside the intended segment.
- Where it is accessible, use the length of the stream to presize the MemoryStream to the correct size.
- Instead of copying out the result via ToArray, grab the underlying buffer via GetBuffer and use that to create the sound source.
This avoids extraneous copying of the array containing the audio.
