Remove fill_fk_xgrid_with_zeros and ensure masking in convolution

[comane]

• Fix a bug due to wrong zeros filling when using hadronic fk tables
• removed the need of fill_fk_xgrid_with_zeros in most of the code. fill_fk_xgrid_with_zeros is only needed by fast_kernel_arrays, this might be useful in the case in which we want to stack them over the data-dimension

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.96%. Comparing base (47ea395) to head (fdf0701).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #441   +/-   ##
=======================================
  Coverage   94.96%   94.96%           
=======================================
  Files          31       31           
  Lines        1649     1650    +1     
=======================================
+ Hits         1566     1567    +1     
  Misses         83       83           

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[comane]

@tgiani I changed this feature which was introduce for stacking purposes for the GP project. Could you check that it does not break anything in your workflow?

[tgiani]

@comane thanks, I ll look at it in the coming days

[tgiani]

Looks good to me. It doesn t break anything in the gp module