🔧 MAINTAIN: Improve repo format

[chrisjsewell]

• add build-system
• update pre-commit
• move from yapf -> black
• update manifest
• add isort
• add codecov
• add testing for multiple python versions
• add mypy configuration
• add tox configuration

[chrisjsewell]

few minor mypy failures that I'll fix later

[ltalirz]

thanks @chrisjsewell ! Looks fine to me, just some comments/questions

I hope @NinadBhat's work so far has not overlapped too much with this (apologies if it did).
In any case, please see this as encouragement to make PRs early ;-)

[chrisjsewell]

I hope @NinadBhat's work so far has not overlapped too much with this (apologies if it did).

yep, and happy to explain any of the additions, and also how to use tox which I highly suggest 😄 (and pre-commit insall)

[chrisjsewell]

Also FYI, this is my .vscode/settings.json:

{
    "editor.rulers": [88],
    "files.exclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/CVS": true,
        "**/.DS_Store": true,
        "**/.mypy_cache": true,
        "**/.pytest_cache": true,
        "**/__pycache__": true,
    },
    "python.pythonPath": ".tox/py38/bin/python",
    "python.formatting.provider": "black",
    "python.languageServer": "Pylance",
}

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@7a8fb8b). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master       #9   +/-   ##
=========================================
  Coverage          ?   88.52%           
=========================================
  Files             ?        6           
  Lines             ?      122           
  Branches          ?        0           
=========================================
  Hits              ?      108           
  Misses            ?       14           
  Partials          ?        0           

Flag	Coverage Δ
pytests	88.52% <0.00%> (?)

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