vectToScore updates

[ghost]

• More closely emulate the behavior of the NVD calculators over the (non-specific) specification
  • Return overall score
  • Return None for temporal/environmental scores when their respective metrics aren't present
• Fix for v2 vector edge case

Resolves SYN-5588

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.10 ⚠️

Comparison is base (ce12c9b) 97.33% compared to head (cdcb14d) 97.24%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3181      +/-   ##
==========================================
- Coverage   97.33%   97.24%   -0.10%     
==========================================
  Files         224      224              
  Lines       44801    44836      +35     
==========================================
- Hits        43609    43600       -9     
- Misses       1192     1236      +44     

Flag	Coverage Δ
linux	97.24% <100.00%> (+<0.01%)	⬆️
linux_replay	?

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Impacted Files	Coverage Δ
synapse/lib/stormlib/infosec.py	99.48% <100.00%> (+0.05%)	⬆️

... and 9 files with indirect coverage changes

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