Add Maximum a Posteriori (MAP)

[BradyPlanden]

Description

This PR adds a MAP cost function with corresponding tests. This cost function has required arguments for the problem class as well as the likelihood class, this allows the MAP class to be agnostic to the likelihood defined as it constructs the class on initialisation.

This PR also updates the codecov job on the test_on_push workflow to v4 with additional options.

Issue reference

Fixes #248 #277

Review

Before you mark your PR as ready for review, please ensure that you've considered the following:

• Updated the CHANGELOG.md in reverse chronological order (newest at the top) with a concise description of the changes, including the PR number.
• Noted any breaking changes, including details on how it might impact existing functionality.

Type of change

• New Feature: A non-breaking change that adds new functionality.
• Optimization: A code change that improves performance.
• Bug Fix: A non-breaking change that addresses an issue.
• Documentation: Updates to documentation or new documentation for new features.
• Refactoring: Non-functional changes that improve the codebase.
• Style: Non-functional changes related to code style (formatting, naming, etc).
• Testing: Additional tests to improve coverage or confirm functionality.
• Other: (Insert description of change)

Key checklist:

• 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 unit tests pass: $ nox -s tests
• The documentation builds: $ nox -s docs

You can run integration tests, unit tests, and doctests together at once, using $ nox -s quick.

Further checks:

• Code is well-commented, especially in complex or unclear areas.
• Added tests that prove my fix is effective or that my feature works.
• Checked that coverage remains or improves, and added tests if necessary to maintain or increase coverage.

Thank you for contributing to our project! Your efforts help us to deliver great software.

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 95.48%. Comparing base (c33c6ac) to head (1d6f893).
Report is 1 commits behind head on develop.

Files	Patch %	Lines
pybop/costs/fitting_costs.py	96.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #275   +/-   ##
========================================
  Coverage    95.47%   95.48%           
========================================
  Files           36       36           
  Lines         2011     2036   +25     
========================================
+ Hits          1920     1944   +24     
- Misses          91       92    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[NicolaCourtier]

Just one comment from my side, thanks @BradyPlanden, nice addition!