Avoid allocations in fmap

[fhagemann]

Should fix #610 (the exact error reported therein), but there might also be some other functions that might have introduced allocations going from julia-1.10 to julia-1.11

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.73%. Comparing base (fab0496) to head (dd288a8).
Report is 28 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #618      +/-   ##
==========================================
+ Coverage   87.07%   87.73%   +0.65%     
==========================================
  Files          28       29       +1     
  Lines        1888     1908      +20     
==========================================
+ Hits         1644     1674      +30     
+ Misses        244      234      -10     

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[mkitti]

Thank you. This looks pretty straightforward.

I'm currently in the process of trying to straighten out CI, but I have this in my queue to review.

[fhagemann]

I mean full credit goes to @N5N3 for coming up with this solution!