Build Docker image for running tests

[jcapona]

Main changes

Add a workflow that builds a Docker image to run the tests locally. It can be used by running:

docker run \
    --rm \
    -it \
    --volume "$PWD":/sdk \
    --workdir /sdk \
    --entrypoint=pytest \
    pitop/sdk-test-runner \
    --verbose

Screenshots (feature, test output, profiling, dev tools etc)

[insert screenshots here]

Other notes (e.g. implementation quirks, edge cases, questions / issues)

-

Manual testing tips

-

Tag anyone who definitely needs to review or help

-

[codecov[bot]]

Codecov Report

Base: 60.38% // Head: 60.42% // Increases project coverage by +0.04% :tada:

Coverage data is based on head (26a4236) compared to base (c615000). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #596 +/- ## ========================================== + Coverage 60.38% 60.42% +0.04% ========================================== Files 149 149 Lines 7402 7402 ========================================== + Hits 4470 4473 +3 + Misses 2932 2929 -3 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `60.42% <ø> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/pi-top/pi-top-Python-SDK/pull/596?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top) | Coverage Δ | | |---|---|---| | [packages/robotics/pitop/robotics/simple\_pid/PID.py](https://codecov.io/gh/pi-top/pi-top-Python-SDK/pull/596/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top#diff-cGFja2FnZXMvcm9ib3RpY3MvcGl0b3Avcm9ib3RpY3Mvc2ltcGxlX3BpZC9QSUQucHk=) | `80.95% <0.00%> (+0.95%)` | :arrow_up: | | [...cs/pitop/robotics/navigation/core/goal\_criteria.py](https://codecov.io/gh/pi-top/pi-top-Python-SDK/pull/596/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top#diff-cGFja2FnZXMvcm9ib3RpY3MvcGl0b3Avcm9ib3RpY3MvbmF2aWdhdGlvbi9jb3JlL2dvYWxfY3JpdGVyaWEucHk=) | `96.42% <0.00%> (+7.14%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pi-top)

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