Increase accuracy for estimate opnorm

[hakkelt]

Minor change to fix CI test fails because estimate_opnorm stops too early in power iterations.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.89%. Comparing base (c8e2903) to head (5a92ac4).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #29       +/-   ##
===========================================
+ Coverage   72.66%   85.89%   +13.22%     
===========================================
  Files          44       45        +1     
  Lines        3077     3063       -14     
===========================================
+ Hits         2236     2631      +395     
+ Misses        841      432      -409     

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