Issue/1 add workflows

[frank113]

Summary

This PR addresses issue #1 by adding discrete linting and testing steps. The main.yml script is structured in a way that other steps can be added as needed.

Example of action summary: https://github.com/frank113/pycountrycode/actions/runs/5428515778

Issues Addressed

• 1

Changes Made

1. Add flake8, black and isort to dependencies
2. Update poetry.lock in accordance with updated pyproject.toml dependencies
3. Update source code to pass linting and formatting checks
4. Ignore flake8 E251 rule in replace_regex helper function
5. Create lint.yml job to be used in the composite main.yml job
6. Employed a matrix-based approach (looping through hyper parameters such as python-version) to testing in test.yml.
7. Create a main.yml script that performs lint checks then tests the code

Considerations

• I expect that the CI actions and processes will evolve as the project matures
• The environment must be setup for each action (i.e. testing on python 3.11 and linting). At the moment the entire CI process is finished in under two minutes
• If we do not wish to use a matrix-based approach to testing we can combine the lint and test jobs into a single job that can re-use setup code. If we want to avoid matrix-based testing at this time we can easily combine the actions into a single workflow
• The decision to split linting and testing in the CI process was informed by a desire for readable output in the case of errors. Due to the size of the project I felt that the small time tradeoff is worth enhanced readability.

Other

Looking forward to working on this package!

[vincentarelbundock]

This is absolutely fantastic! Thanks so much for your time and efforts, @frank113 !

Also, I'll copy a lot of this to my {marginaleffects} package port, so this is a 2-for-1 contribution :)