Add client and kernel coverage from robot tests

[nrbgt]

Checklist

• the PR target is correct
  • main for releases, docs-only fixes and post-release hot-fixes
  • dev for everything else
• ran doit lint locally

References

• includes Postmortem for 0.3.2 #87
• fixes Gather client, kernel, and server coverage during acceptance tests #88

Code changes

• add python-dotenv
• do instrumented build when TOTAL_COVERAGE is set
• gather coverage from browser during robot tests
• run kernels with coverage
• generate atest only and combined (atest + utest) coverage
• run full suite under coverage in CI

User-facing changes

n/a

Backwards-incompatible changes

n/a

Screens

note	screen
combined py
js

[github-actions]

Try it on ⬅️ ReadTheDocs or Binder ➡️

[sanbales]

Did a quick pass over the code changes. Looked good to me.

[sanbales]

Looks good to me! I'm on travel without much of a chance to do a thorough review, but tests are passing and changes look good.