Testing of Kernels and execution loop

[VeckoTheGecko]

Now that we are poking around the kernel loop (#2107), it would be really helpful to make sure that the v4 test suite is fleshed out here so that we can pick up regressions and changes in behaviour. It would be good to:

• Migrate v3 tests re. kernels and pset execution across to v4
• Make sure that all kernels in parcels/application_kernels/advection.py are tested (at least just running them)
• Add tooling to hash arrays of floats (allowing for easy comparison between commits, without having to store full output)

[VeckoTheGecko]

Closed via #2113