Avoid creating a new generator to create `LittleDict` for every equation

[KristofferC]

This takes the time to precompile the FRB_US model from 52s to 38s.

This also takes the load time of the precompiled FRB_US model from 5.5s to 0.16s which is a bigger change than I expected.

[codecov-commenter]

Codecov Report

Merging #32 (ffb4218) into master (32835b1) will not change coverage. The diff coverage is n/a.

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@@           Coverage Diff           @@
##           master      #32   +/-   ##
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  Coverage   94.20%   94.20%           
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  Files          15       15           
  Lines        1675     1675           
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  Hits         1578     1578           
  Misses         97       97           

Impacted Files	Coverage Δ
src/evaluation.jl	80.33% <ø> (ø)

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[bbejanov]

Wow, I just found out last week how costly generators are. Thanks for fixing this @KristofferC! https://discourse.julialang.org/t/slow-dict-comprehension/94797

[KristofferC]

Heh, in one of the replies in https://discourse.julialang.org/t/slow-dict-comprehension/94797/5?u=kristoffer.carlsson

So I would say you’re fine using a comprehension in practice. It’s unlikely you’ll have hundreds of these in your top-level script?