Fix optimise methods returning incorrect best_pos

[ichbinjakes]

Description of changes

Fix:

• BinaryPSO returning correct best_pos
• GeneralPSO returning correct best_pos
• LocalBestPSO returning correct best_pos
• GlobalBestPSO returning correct best_pos

Tests:

• Added simple test cases for each optimiser
  • I have no experience using pytest but tests work, I can add tests using unittest if needed.

Flake8 / Black reformatted some other code

Related Issue

#321

Motivation and Context

Bug fix

How Has This Been Tested?

Tested using unittest, then "ported' to the pytest files. All test passed.
Followed instruction in contributing.rst, except used new conda env.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [?] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project. Tests work but don't match code style
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[whzup]

Very nice to see a PR of you, @ichbinjakes!👍🎊💯 There are some things that I think could be made easier (see comments in the code).

[whzup]

This seems good to me 👍 Thank you for your PR @ichbinjakes. Hope you had fun working on it 😄🎊

[ljvmiranda921]

Can you squash-merge this, @whzup ? Thank you @ichbinjakes !

[ljvmiranda921]

Nice!! Thank you again, @ichbinjakes , and to @whzup for conducting the review! I'll be updating the contributor's list this weekend!

[ljvmiranda921]

@allcontributors[bot] please add @ichbinjakes for bug and code

[allcontributors]

@ljvmiranda921

I've put up a pull request to add @ichbinjakes! 🎉