Fixes #443 and #364

# Description

* Adds clipping method to ``imod.msw.MetaSwapModel``, this includes a
special case for ``clip_box`` method of PrecipitationMapping, and
EvapotranspirationMapping: These should not be clipped if a
``MeteoGridCopy`` instance is part of the model. Otherwise nonsensical
mappings are generated.
* Add ``imod.msw.MetaSwapModel.clip_box`` method to public API
* Override ``clip_box`` method in MeteoMapping, should clip meteo
attribute instead of dataset attribute.
* Refactor: Move time slice clipping logic to
``imod.common.utilities.clip``.
* Refactor: Make ``meteo`` class variable an attribute. This makes more
sense. I think I made it a class variable before to please mypy.
* Boyscouting: Add some extra docstring information on usecase to
``imod.msw.MeteoGridCopy``

# Checklist
- [x] Links to correct issue
- [x] Update changelog, if changes affect users
- [x] PR title starts with ``Issue #nr``, e.g. ``Issue #737``
- [x] Unit tests were added
- [ ] **If feature added**: Added/extended example