Add multi-hypothesiser based MFA with multi-model example

[sdhiscocks]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 98.52941% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.05%. Comparing base (3ad3eb6) to head (3baf40e).

Files with missing lines	Patch %	Lines
stonesoup/hypothesiser/mfa.py	97.82%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1216      +/-   ##
==========================================
+ Coverage   93.99%   94.05%   +0.06%     
==========================================
  Files         227      227              
  Lines       15764    15808      +44     
  Branches     2177     2182       +5     
==========================================
+ Hits        14817    14869      +52     
+ Misses        657      654       -3     
+ Partials      290      285       -5     

Flag	Coverage Δ
integration	66.68% <98.52%> (+0.10%)	⬆️
unittests	91.48% <95.58%> (+0.06%)	⬆️

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[hpritchett-dstl]

Only thing i can think of is to vectorize the multivariate normal logpdf calculation in each PDAHypothesiser. hypothsise call. We could potentially call each hypothesiser's predictor's predict and do one single vectorized batch_multivariate_normal_logpdf in MFAHypothesiser.hypothesise , and have these cached. I can see how this added bloat won't merit the speed increase though.