Base Bayesian framework with EP-BOLFI integration

[YannickNoelStephanKuhn]

Description

Adds support for multivariate parameter distributions and Bayesian optimisers. Included is the integration for EP-BOLFI as a first example for other Bayesian optimisers.

Fixes #585
Replaces pull request #786

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #).

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: $ pre-commit run or $ nox -s pre-commit (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: nox -s tests
• The documentation builds: nox -s doctest
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

❌ Patch coverage is 16.33333% with 251 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.91%. Comparing base (4628a65) to head (f8785a7).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
pybop/optimisers/ep_bolfi_optimiser.py	0.00%	116 Missing ⚠️
pybop/costs/parameterised_costs.py	0.00%	74 Missing ⚠️
pybop/parameters/multivariate_distributions.py	52.23%	32 Missing ⚠️
pybop/parameters/multivariate_parameters.py	31.25%	22 Missing ⚠️
pybop/_result.py	36.36%	7 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #846      +/-   ##
===========================================
- Coverage    89.41%   84.91%   -4.51%     
===========================================
  Files           63       67       +4     
  Lines         4857     5170     +313     
===========================================
+ Hits          4343     4390      +47     
- Misses         514      780     +266     

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