Use extracted (alpha) connection library

[microbit-matt-hillsdon]

This PR is expected to hang around for a bit as we evolve the connection library interface.

Issues specific to the integration:

• [ ] x2 deps on Intel hex library (due to fixed version dep?)
• [ ] bundle size check needed. The connection lib includes hex-related dep that we don't use - is it bundled?

[github-actions[bot]]

Preview build will be at https://review-python-editor-v3.microbit.org/connection/

[microbit-matt-hillsdon]

Everything seems to be working OK as of https://github.com/microbit-foundation/python-editor-v3/pull/1190/commits/ec290dd14b6e19024cd2f19373fa3b6e24a6011b