error handling: Refactor how "Input too long" errors are handled.

[briansmith]

Handle "input too long" errors consistently across the digest and bits modules. This is a step towards more modules doing the same.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 97.16%. Comparing base (0a00284) to head (e43a335).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tests/bits_tests.rs	84.21%	3 Missing ⚠️
src/digest.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2202      +/-   ##
==========================================
- Coverage   97.18%   97.16%   -0.02%     
==========================================
  Files         156      158       +2     
  Lines       20217    20232      +15     
  Branches      454      454              
==========================================
+ Hits        19647    19658      +11     
- Misses        465      470       +5     
+ Partials      105      104       -1     

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