sysaudio: @sizeOf(T) is not the same as @bitSizeOf(T)

[ypsvlq]

In #1152, @sizeOf(i24) == 4 was considered a Zig bug, but the Zig documentation suggests this is not the case:

This size may contain padding bytes. If there were two consecutive T in memory, the padding would be the offset in bytes between element at index 0 and the element at index 1. For integer, consider whether you want to use @sizeOf(T) or @typeInfo(T).Int.bits.

The correct approach presumably involves using std.PackedIntSlice or similar in convert{To,From}, but exactly how this should be implemented is not clear. Alternatively, it might be possible to replace i24 with i24_4b (removed in hexops/mach-sysaudio@0a6bb12) (EDIT: after minor testing this does not seem to work)