chore: lock cross to msrv

[gpeacock]

ci failures were caused since cross was not locking to the the minumum supported rust version.

Also added a msrv tag so we don't repeat the constant in ci.yml

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.15%. Comparing base (da629e6) to head (8605e3c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   65.15%   65.15%           
=======================================
  Files           2        2           
  Lines         815      815           
=======================================
  Hits          531      531           
  Misses        284      284           

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