Update pressure tests and fix sqrt grid error in Numerov

[timcallow]

Due to a mix up this PR actually fixes two separate issues:

• Pressure tests include potential for virial method
• For final grid point propagation, fixed for sqrt grid

[codecov]

Codecov Report

Merging #187 (8901717) into develop (2de4ecd) will decrease coverage by 5.59%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop     #187      +/-   ##
===========================================
- Coverage    97.24%   91.66%   -5.59%     
===========================================
  Files           14       14              
  Lines         2362     2364       +2     
===========================================
- Hits          2297     2167     -130     
- Misses          65      197     +132     

Impacted Files	Coverage Δ
atoMEC/numerov.py	87.27% <66.66%> (-8.15%)	⬇️

... and 5 files with indirect coverage changes