Fix voice example for DCA0 audio

[cactysman]

When I first learned of DCA back in April and checked out the example in this repository, I grew quite frustrated (and many others probably have, too) since none of the DCA files I created myself using the original Go program following its manual worked at all but the nico.dca test file that is included in here happened to work just fine.

I decided to have a closer look at it and realized that, for some obscure reason, its headers use 4 bytes as opposed to the actual int16 type header the original DCA tool produces.

I've done a bit of research, assuming nico.dca might have been created with an older iteration of DCA or something, but I couldn't really find anything specifying a header size other than 2 bytes.

Anyways, this here fixes the writeOpus function in the voice example, now correctly reading DCA0 files.

In the second commit I also included a bit of logic detecting and properly mitigating 4-byte-header DCA0 files in case they're actually more common than how it seems. If that's not desired, I can easily just trim back the branch and update nico.dca to use 2-byte headers instead.

[topi314]

While I do appreciate the effort you put into fixing this
I am not exactly sure I want to implement a full spec compliant DCA reader in here

How about just documenting it expects DCA0 4 bytes? 😅

[topi314]

just checked this pr again after a good night sleep.
so apparently nico.dca uses 4 bytes (uint32) instead of 2 bytes (int16) headers.
I copied that file from a different repo at that time (including the code to parse it).

Feel free to re-encode it as 2 bytes (int16) header & adjust the code to read that too lol
also please add a comment saying it expects DCA0

[topi314]

thanks!