Add support for rm2fb

[danshick]

This makes reStream work with rm2fb

When installed, rm2fb creates /dev/shm/swtfb.01, which behaves very much like the old /dev/fb0 from the rm1. To get this working, a conditional check for this file was added both to the rust binary as well as the shell script.

Additionally, I've PR'd the rust helper binary into toltec. It has been accepted into testing. If installed via toltec, the rust helper binary will end up at /opt/bin/restream. I've also made two small changes to support this additional location for the helper.

[rien]

Are there improvements noticeable when using the rm2fb instead of reading the process memory?

Your PR is great, but the logic for checking whether to use the alternative framebuffer makes things complicated... I'd rather not add complexity when there is no noticeable improvement.

Adding restream to toltec is great! I should start using versioning for restream!

[Eeems]

While this adds complexity, it also makes reStream usable for users who are using rm2fb in order to use other third party software. Otherwise reStream only works for xochitl without rm2fb installed.

[rien]

Please reopen this PR against the new main branch.

[rien]

While this adds complexity, it also makes reStream usable for users who are using rm2fb in order to use other third party software. Otherwise reStream only works for xochitl without rm2fb installed.

reStream currently already works for users who are using rm2fb if I'm not mistaken?

Aha I know see the problem: users running custom software (that's not xochitl). Then this is indeed needed.