Consider using {evaluate} in place of capture_expr_output

[dgkf]

I just recently discovered this evaluate package, which seems to aim to solve the same problem that capture_expr_output solves. Unlike capture_expr_output, evaluate has years of development behind it with contributions from many very well established folks in the R space.

I contributed capture_expr_output at a time when we were still experimenting with this ability to log metric evaluation and wasn't aware that there were better solutions out there. Although I'm reasonably satisfied with where the code ended up, it's always felt like it could be a problematic and complex bit of code to try to maintain. It might be worth swapping it out to have some reassurance that we can look for some help from some very talented folks to help support this feature.

[emilliman5]

See #350