Release 0.18.20

- Remove the Corpuscles dependency; neutrino PDG codes are now hardcoded.
  This also drops Unitful/UnitfulAtomic and eliminates load-time recompilation.
- Move HDF5 into a package extension (KM3ioHDF5Ext). using KM3io no longer
  pulls in the HDF5/MPICH stack; HDF5 features now require `using HDF5`.
- Add a PrecompileTools workload so the first ROOTFile open/read is ~2.4x faster.
- Convert the Cherenkov-times docs example from PGFPlotsX to CairoMakie.
- Add diff tools (compare, Diff, FieldChange, ...).
- Fix aux test.