Fix for lattice energy UnitConv bug

[T-Nicholls]

Also a bonus commit used by Python BBA

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.11%. Comparing base (c32f154) to head (27571aa).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #144      +/-   ##
==========================================
- Coverage   99.48%   99.11%   -0.38%     
==========================================
  Files          12       12              
  Lines         775      788      +13     
==========================================
+ Hits          771      781      +10     
- Misses          4        7       +3     

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[T-Nicholls]

Ok, CI failures are resolved and I've cleaned up the commit history so this is ready to merge

However, we should get Pytac properly on the latest Copier template at some point

[ptsOSL]

I agree that we need to convert this to copier template, probably a job for me alongside converting slow feedbacks.

[MJGaughran]

I think you've both highlighted several existing problems in pytac (e.g. with type hinting), but I agree that this PR is not making things worse than before.

Otherwise, it all looks fine.