Improve integration testing

[studioph]

Closes #5

The following updates have been made:

• The build workflow has been split into a reusable docker build workflow (docker.yml) and the main build jobs (build.yml)
• A new integration workflow has been created that will run after a PR is merged into the main branch
  • The workflow runs against 0.9 and 0.10 versions of beartype
  • The workflow installs bearboto3 both with and without the mypy type stubs as extras
  • The above is on top of the 4 supported python versions, meaning there are 16 integrations running to ensure maximum compatibility!
• The integration project has been updated to install bearboto3 from git, eliminating the need to build/publish just for testing and it will always be up to date
• lint_and_test has been split back into separate lint and test jobs as that seemed like better practice, instead of trying to hyper-optimize the jobs by running them in the same container to avoid the overhead of pulling the image twice.

[leycec]

The above is on top of the 4 supported python versions, meaning there are 16 integrations running to ensure maximum compatibility!

Beartype Man is impressed at this fearsome display of combinatorics gone wild. 😮

Luckily, beartype 0.11.0 is unlikely to land for at least a few months. We're currently hip-deep in beartype 0.10.x patch release hell heaven – with no exit strategy in sight. So let the fun times roll.