Returns the expected (not actual) size of `data` in number of bytes, depending on the type of the command.

The following error-checking functions were copy&pasted from the OpenEXR source code

The following error-checking functions were copy&pasted from the OpenEXR source code

The coroutine is about to complete (via co_return, reaching the end of the coroutine body, or an uncaught exception). The awaiter returned here define