Add bitfield Display regression tests

[macladson]

Adds a small regression test for bitfield's Display impl

Note that the blitlist uses a bit_len of 15 to check if trailing zeros are removed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.62%. Comparing base (f9286b5) to head (6a59af1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #60      +/-   ##
==========================================
+ Coverage   75.75%   76.62%   +0.87%     
==========================================
  Files          14       14              
  Lines         800      800              
==========================================
+ Hits          606      613       +7     
+ Misses        194      187       -7     

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