fix: make r_device.fields a constant pointer

[obones]

This allows for static "output_fields" to be stored in readonly memory on embedded architectures saving the very limited RAM available.
This saves about 7kB, representing 2.3% of the total installed RAM, which may not sound much but makes quite a difference for other parts of the program.

[zuckschwerdt]

The clang-format wants the asterisk to stick, e.g. static char const *const output_fields[] = {

[obones]

Bummer, I did not notice any issue from the 5 actions that have run, I'll fix that

[zuckschwerdt]

I did once try to check/enforce clang-format, but we have too much "special formatting" in the code still. It's not checked for now. But the idea is to have it automated once some problems with .clang-format have been solved (i.e. clang-format should pass more code through unmodified and not e.g. change so many linebreaks and indents).

[obones]

Thanks for the explanation about clang-format, I have learnt a new thing here.
I have amended the last commit, I believe this is now correct.