feat: optional replacement semantics for stress period data

[wpbonelli]

Add an optional parameter replace=False to the .set_data() methods on the stress period data model. Setting this True resets the data before setting provided keys, i.e. clears all preexisting entries rather than leaving them in place.

Since stress period configuration is not stored solely in the underlying data model but also in package block headers, a trap is necessary in MFBlock.write() to sync block headers to the keys existing in the period data, to avoid writing empty/spurious period blocks.

Suggested in #2663 (comment)

[codecov]

Codecov Report

❌ Patch coverage is 97.67442% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.6%. Comparing base (556c088) to head (37dd348).
⚠️ Report is 91 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/mf6/data/mfdataarray.py	90.0%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2664      +/-   ##
===========================================
+ Coverage     55.5%    72.6%   +17.1%     
===========================================
  Files          644      667      +23     
  Lines       124135   129426    +5291     
===========================================
+ Hits         68947    94065   +25118     
+ Misses       55188    35361   -19827     

Files with missing lines	Coverage Δ
flopy/mf6/data/mfdatalist.py	66.3% <100.0%> (-3.0%)	⬇️
flopy/mf6/data/mfdataplist.py	74.1% <100.0%> (-4.8%)	⬇️
flopy/mf6/mfpackage.py	68.7% <100.0%> (-12.9%)	⬇️
flopy/mf6/data/mfdataarray.py	59.4% <90.0%> (-7.6%)	⬇️

... and 555 files with indirect coverage changes

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