WIP: Allow cycles for material preview rendering

I use SAM mostly to manage procedural materials, some of which don't render as well with EEVEE, so I started working on Cycles support in SAM. This is specifically for materials so far, where it makes the most sense in my opinion. The feature is turned off by default and can be toggled with a checkbox in the add-on preferences.

This isn't well tested yet. It worked for rerendering my material previews, but there might be some potential bug when having mixed (EEVEE and Cycles) workloads in preview rendering.

I thought I'll throw this out here regardless, in case it aligns with your idea for future development of SAM. If there are any remaining issues with this patch, I'd be happy to iron these out.