Xobjects

**Changes:**

- Minor linting

**Full Changelog**: https://github.com/xsuite/xobjects/compare/v0.1.28..v0.1.30

**Changes:**

- Implement `to_nparray` and `to_json` and add suitable tests for xobjects. The method `to_json` returns a dict that is json-compliant from which the xobjects can be regenerated simply by passing the dict to the constructor.
- Avoid memcopy (where possible) in a hybrid class.
- Make contexts visible in test printout. Parametrize tests over contexts simply by adding `for_all_test_contexts` or `for_all_test_contexts(excluding: Iterable[str] | str)` on them, the context is passed as `test_context` to the test.
- Minor fixes of typos.

**Full Changelog**: https://github.com/xsuite/xobjects/compare/v0.1.27...v0.1.28

**Changes:**
- Add _update method to class to avoid overwriting arrays.
- Ensure that NULL is defined in pyopencl contexts.

**Full Changelog**: https://github.com/xsuite/xobjects/compare/v0.1.26...v0.1.27

**Changes:**
- Fix: pyopencl deprecated syntax

**Full Changelog**: https://github.com/xsuite/xobjects/compare/v0.1.25...v0.1.26

**Changes:**
- Version number accessible as xobjects.__version__
- Fix in Array C API generation
- Buffer/context consistency check on allocate_on_buffer

**Changes:**
- Faster array initialisation
- Introduced xobjects.get_a_buffer function