Orbital optimisation

[obackhouse]

Adds orbital optimisation, includes a refactor to Brueckner orbital self-consistency and some minor fixes.

• Unit tests
• Check correctness c.f. literature
• Backend support, need to redirect scipy.linalg.expm and scipy.linalg.logm?

[codecov]

Codecov Report

Attention: Patch coverage is 39.37008% with 308 lines in your changes missing coverage. Please review.

Project coverage is 89.44%. Comparing base (7c01c64) to head (8741a99).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
ebcc/opt/gopt.py	17.94%	95 Missing and 1 partial ⚠️
ebcc/opt/uopt.py	47.58%	67 Missing and 9 partials ⚠️
ebcc/opt/base.py	34.31%	67 Missing ⚠️
ebcc/opt/ropt.py	48.71%	52 Missing and 8 partials ⚠️
ebcc/cc/base.py	54.54%	5 Missing ⚠️
ebcc/ham/space.py	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
- Coverage   89.61%   89.44%   -0.17%     
==========================================
  Files         101      101              
  Lines      114503   114763     +260     
  Branches      759      794      +35     
==========================================
+ Hits       102611   102655      +44     
- Misses      11658    11872     +214     
- Partials      234      236       +2     

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