refactor(msfsr2): write sfr_botm_conflicts.chk to model workspace

[wpbonelli]

• close MFSFR2 assign_layers hardcoded output path #1471

[codecov]

Codecov Report

Merging #2002 (f0e67d0) into develop (af8954b) will increase coverage by 0.0%.
The diff coverage is 50.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2002   +/-   ##
=======================================
  Coverage     72.7%   72.7%           
=======================================
  Files          258     258           
  Lines        58828   58828           
=======================================
+ Hits         42797   42798    +1     
+ Misses       16031   16030    -1     

Files	Coverage Δ
flopy/modflow/mfsfr2.py	87.5% <50.0%> (ø)

... and 1 file with indirect coverage changes