Implement airspeed velocity for monitoring esmf-regrid performance

[jamesp]

✨ Feature Request

We should add airspeed velocity performance testing to this package so that we can monitor performance improvements over time.

[github-actions]

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[trexfeathers]

Agreed steps from conversation with @stephenworsley:

• Sort out ASV architecture - @trexfeathers working on a PR right now.
• Write first benchmarks - using sample cube-spheres from SciTools/iris-test-data.
• Joint and separate experiments with:
  • asv continuous
  • asv gh-pages
• Apply improved knowledge to decisions on:
  • If/how we integrate some/all benchmarks into continuous integration runs.
    Intelligent use of ASV's repeats should probably provide statistical rigour to compensate for possible risks of running on shared architecture.
  • If we run some/all benchmarks overnight on local hardware.
  • What results we publish, and where.

[trexfeathers]

We now have a minimum architecture in place (follow the breadcrumbs from here), which allows for easy addition of new benchmarks, which form part of the standard CI.

There is the outstanding matter of publishing the results - #90 - but this can come later.