Add vectorized jprod

[blegat]

This fixes the regression on the on the control7 SDPLib benchmark for kocvara/Loraine.jl#29

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.30%. Comparing base (50db875) to head (e74680b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   99.27%   99.30%   +0.02%     
==========================================
  Files          21       21              
  Lines         969     1007      +38     
==========================================
+ Hits          962     1000      +38     
  Misses          7        7              

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