[Perf] Bottlenecks from profiling

[dshemetov]

Recent profiling profvis_arduous.dingo_20240815.html.zip from exploration-tooling uncovered a couple slow spots in the code here:

• this mold_recipe line that calls into a hardhat internal
• and this post-join error verification in layer_population scaling, the slow line being the grepl after the join

I totally don't understand what's going on in (1), but @dsweber2 says @dajmcdon might rewrite that function at some point.

(2) seems like an incorrect use of try catch - the output of the try line is either an error or a tibble, but in either case it runs grepl on the result, which, in the latter case is quite slow. That should be a simple fix: catch the error and grepl only then.

[dajmcdon]

@dshemetov for (2), this function needs to be refactored. See #234 maybe also #248