Modify BadInputSetWarning logic for relaxations of a likely metal

[Andrew-S-Rosen]

Closes #726.

Relaxing a metal with ISMEAR = 0 is fine, as noted in the VASP manual, provided SIGMA is sufficiently small (< 0.05 is the recommendation in the VASP manual).

If you have no a priori knowledge of your system, for instance, if you do not know whether your system is an insulator, semiconductor or metal then always use Gaussian smearing ISMEAR=0 in combination with a small SIGMA=0.03-0.05.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (62ae659) 76.19% compared to head (fc165eb) 76.10%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #727      +/-   ##
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- Coverage   76.19%   76.10%   -0.09%     
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  Files          87       87              
  Lines        7178     7186       +8     
  Branches     1057     1059       +2     
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  Hits         5469     5469              
- Misses       1388     1396       +8     
  Partials      321      321              

Files	Coverage Δ
src/atomate2/vasp/sets/base.py	73.08% <0.00%> (-1.48%)	⬇️

[janosh]

thanks @Andrew-S-Rosen ! this is helpful. do the changes i made look correct?

[Andrew-S-Rosen]

Yes, that looks right. Thanks, @janosh. Sorry I was too lazy to split the messages myself 😅

FYI: I made the same PR in materialsproject/pymatgen#3634