Remove creation of temporary files

[GalaxyShard]

It appears mmutil is using files to pass arguments between functions globally. Currently these files (named sampJ328G54AU3.tmp and songDJ34957FAI.tmp) are created in the working directory, and as a result this causes issues when running mmutil in parallel within the same directory; mmutil attempts to access the file created by other instances of mmutil, causing odd audio bugs in the output.

I currently have a patch that allows overriding the path of the temporary file (so that it can be placed in the proper temporary directory like /tmp on linux) (GalaxyShard@5961920), although it appears that removing the creation of the files altogether might be a bit more involved.

[AntonioND]

Overriding the path looks like a very fragile fix. If a build system wants to run multiple instances of mmutil at the same time, the build system needs to pass the name, which is a bad idea.

Wouldn't it be better to open a file mapped in RAM? We could use fmemopen() https://pubs.opengroup.org/onlinepubs/9799919799/functions/fmemopen.html or similar so that we don't have to modify the code that much.

But yeah, because of this issue I had to add a workaround to my build system: https://github.com/AntonioND/architectds/blob/7aa01b1f1366b674bc8cae32443909fefa862f02/architectds/architectds.py#L1978-L1986