avoid std::prelude imports

[cpu]

This also means the panic macro isn't ambiguous so we can drop explicit panic imports.

Follow-up to #449

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.72%. Comparing base (25dc5ee) to head (e945bae).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #450   +/-   ##
=======================================
  Coverage   96.72%   96.72%           
=======================================
  Files          20       20           
  Lines        3903     3903           
=======================================
  Hits         3775     3775           
  Misses        128      128           

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