Use local tempfiles from withr

[juliasilge]

The functions in withr for temp files and temp directories clean up after themselves, which is what we are looking for. It's a low dependency package that we now use across multiple bundling methods, so let's move it to Imports.

[juliasilge]

We could use withr::defer() for the torch bundler but it wouldn't really change or improve it that much.

[juliasilge]

Addresses #40