Hybrid upwind

[enricoballini]

This PR adds the hybrid upwind discretization scheme following https://doi.org/10.1016/j.cma.2021.114288

• Minor change (e.g., dependency bumps, broken links).
• Bugfix (non-breaking change which fixes an issue).
• [x ] New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• Testing (contribution related to testing of existing or new functionality).
• Documentation (contribution related to adding, improving, or fixing documentation).
• Maintenance (e.g., improve logic and performance, remove obsolete code).
• Other:

Checklist

Put an x in the boxes that apply or explain briefly why the box is not relevant.

• The documentation is up-to-date.
• Static typing is included in the update.
• This PR does not duplicate existing functionality.
• The update is covered by the test suite (including tests added in the PR).
• If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.

[keileg]

Thanks, @enricoballini. As we agreed, @OmarDuran and I will have a look at this in due course, likely doing (substantial) changes, but the burden is off your shoulders.

[keileg]

@OmarDuran I formally converted this to draft, since it may take some time before we have the capacity to work on this.