Fix linter complaints

[arik-so]

The linter is currently complaining about map_err where inspect_err is possible, as well as about a dependency_on_unit_never_type_fallback issue.

[tnull]

inspect_err doesn't exist on MSRV of 1.63, IIUC.

[arik-so]

Yup, changed it to suppressing the warnings instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.10%. Comparing base (23109b6) to head (d340ac3).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3334      +/-   ##
==========================================
+ Coverage   89.61%   90.10%   +0.48%     
==========================================
  Files         126      126              
  Lines      102690   106287    +3597     
  Branches   102690   106287    +3597     
==========================================
+ Hits        92028    95772    +3744     
+ Misses       7923     7842      -81     
+ Partials     2739     2673      -66     

Flag	Coverage Δ
	90.10% <ø> (+0.48%)	⬆️

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[arik-so]

Alternatively, we could run the linter on 1.63?