fix(binaryfile): fix head/budget file reversal

[wpbonelli]

Following up on #2475. Fixes #2473. #2480 was extracted from this changeset for tidiness.

Up to now the reversal methods have worked for our backwards particle tracking examples, which have very simple time discretizations. But they didn't work in the general case — only for "symmetric" tdis with no time step multiplier.

Fix several issues with binary output file reversal. Clean up and expand tests to include dis/disv/disu with both trivial and a couple non-trivial time discretizations. Make a small (but consequential) fix for #2481: when reversing we need to take the reciprocal of tsmult. Fix an issue with the ModelTime class perioddata property and add a pertim property like the totim property.

[codecov]

Codecov Report

Attention: Patch coverage is 45.74468% with 51 lines in your changes missing coverage. Please review.

Project coverage is 76.0%. Comparing base (bb9824e) to head (7fc3c97).
Report is 73 commits behind head on develop.

Files with missing lines	Patch %	Lines
flopy/utils/binaryfile/reverse.py	0.0%	47 Missing ⚠️
flopy/discretization/modeltime.py	71.4%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2483     +/-   ##
=========================================
+ Coverage     68.4%   76.0%   +7.6%     
=========================================
  Files          294     296      +2     
  Lines        59390   64137   +4747     
=========================================
+ Hits         40652   48790   +8138     
+ Misses       18738   15347   -3391     

Files with missing lines	Coverage Δ
flopy/utils/binaryfile/__init__.py	85.4% <100.0%> (ø)
flopy/discretization/modeltime.py	77.0% <71.4%> (+27.0%)	⬆️
flopy/utils/binaryfile/reverse.py	0.0% <0.0%> (ø)

... and 257 files with indirect coverage changes

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