Feature/verification tests

[fluidnumericsJoe]

Description

This PR adds new generated unstructured datasets to assist in verification of interpolation and time integration schemes when applied to unstructured grids. The datasets define flow fields for uniform translation and solid body rotation. Uniform translation (constant velocity fields) is exact under all built-in interpolation and time integration schemes; included tests verify that particle trajectories are exact to machine precision. The solid body rotation fields are exact for node registered velocity fields with piecewise linear interpolation and the included tests demonstrate this

Checklist

• Tests added
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it (e.g., by pasting your prompt): Claude code was used to translate python notebooks from https://github.com/FluidNumerics/parcels-ux-validation-verification to generate generic datasets and tests. Generated code was reviewed and tested.