ENH: Add memory estimate for first-level models, enable memory management

[effigies]

Groundwork for #165.

[codecov-io]

Codecov Report

Merging #199 into master will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
- Coverage    76.2%   76.17%   -0.03%     
==========================================
  Files          18       18              
  Lines        1017     1020       +3     
  Branches      179      180       +1     
==========================================
+ Hits          775      777       +2     
  Misses        150      150              
- Partials       92       93       +1

Flag	Coverage Δ
#ds003	76.17% <66.66%> (-0.03%)	⬇️

Impacted Files	Coverage Δ
fitlins/workflows/base.py	60.43% <ø> (ø)	⬆️
fitlins/cli/run.py	79.64% <66.66%> (-0.36%)	⬇️

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