Remove unused field from PseudoJet

[graeme-a-stewart]

The _inv_pt2 field in the PseudoJet struct was unused and had no accessor. It is removed.

A few cycles will be saved, but there is no measurable impact on standard benchmarks.

Closes #225.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.05%. Comparing base (04faf06) to head (dea4352).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #226      +/-   ##
==========================================
- Coverage   82.07%   82.05%   -0.02%     
==========================================
  Files          21       21              
  Lines        1400     1399       -1     
==========================================
- Hits         1149     1148       -1     
  Misses        251      251              

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[m-fila]

Thanks, LGTM!

[graeme-a-stewart]

Thanks, LGTM!

Thanks to you for having spotted it 👀