fix(float32, empty stress period): #1779 and #1793

[spaulins-usgs]

Fixed issue where flopy only recognized float64 data and not float32 data.

Fixed issue where block headers were not getting created for empty data blocks.

[codecov]

Codecov Report

Merging #1806 (5f60eb1) into develop (badc431) will decrease coverage by 0.1%.
The diff coverage is 90.0%.

@@            Coverage Diff            @@
##           develop   #1806     +/-   ##
=========================================
- Coverage     72.1%   72.1%   -0.1%     
=========================================
  Files          254     254             
  Lines        55929   55971     +42     
=========================================
+ Hits         40377   40395     +18     
- Misses       15552   15576     +24     

Impacted Files	Coverage Δ
flopy/mf6/data/mfdatastorage.py	70.4% <ø> (ø)
flopy/mf6/mfpackage.py	66.5% <84.6%> (+0.3%)	⬆️
flopy/mf6/data/mfdata.py	75.6% <100.0%> (+<0.1%)	⬆️
flopy/mf6/data/mfdataarray.py	60.9% <100.0%> (-1.9%)	⬇️
flopy/mf6/data/mfdatalist.py	73.3% <100.0%> (ø)
flopy/mf6/data/mfdatascalar.py	60.1% <100.0%> (+0.1%)	⬆️

... and 8 files with indirect coverage changes