fix(mfpackage): modify maxbound evaluation

[jdhughes-usgs]

Modified the way maxbound is evaluated relative to the size of the stress_period_data data. If maxbound is defined to be something other than None when a package is initialized the value is only modified if the sized of the stress_period_data exceeds the specified maxbound value. This change was precipitated by the need to set a maxbound value larger than the largest size of stress_period_data for use with the MODFLOW API.

This change also simplifies the three value boolean check that was used previously.

[codecov]

Codecov Report

Merging #1530 (534322a) into develop (f45c8f9) will decrease coverage by 1.3%.
The diff coverage is 100.0%.

@@            Coverage Diff            @@
##           develop   #1530     +/-   ##
=========================================
- Coverage     72.4%   71.1%   -1.4%     
=========================================
  Files          251     251             
  Lines        54163   52836   -1327     
=========================================
- Hits         39255   37580   -1675     
- Misses       14908   15256    +348     

Impacted Files	Coverage Δ
flopy/mf6/mfpackage.py	63.3% <100.0%> (-4.0%)	⬇️
flopy/mf6/modflow/mfgwtgwt.py	33.3% <0.0%> (-29.8%)	⬇️
flopy/mf6/modflow/mfgwfcsub.py	39.0% <0.0%> (-28.2%)	⬇️
flopy/mf6/modflow/mfgwtlkt.py	45.7% <0.0%> (-24.6%)	⬇️
flopy/mf6/modflow/mfgwtmwt.py	45.7% <0.0%> (-24.6%)	⬇️
flopy/mf6/modflow/mfgwtsft.py	45.7% <0.0%> (-24.6%)	⬇️
flopy/mf6/modflow/mfgwtuzt.py	45.7% <0.0%> (-24.6%)	⬇️
flopy/mf6/modflow/mfgwtcnc.py	46.1% <0.0%> (-23.5%)	⬇️
flopy/mf6/modflow/mfgwtsrc.py	46.1% <0.0%> (-23.5%)	⬇️
flopy/mf6/modflow/mfgwfapi.py	47.3% <0.0%> (-22.4%)	⬇️
... and 87 more

[jdhughes-usgs]

@spaulins-usgs could you take a look at this PR today. Some work I am doing with the MODFLOW API for the New York Water Science Center is dependent on this change. I ran all of the tests locally that are not run as part of the standard CI workflows and they passed.