Refnx

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- Modify to allow loading of .ORB ORSO files.
- Capability for calculating PNR theoretical curves.
- Fix some tests for new periodictable release.
- Stop using deprecated setuptools module.
- Analysis for polarised neutron reflectometry.

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- put black configuration in pyproject.toml
- put ruff configuration in pyproject.toml
- fix bug in ManualBeamFinder, must be a matplotlib thing
- Add LipidLeafletGuest, a LipidLeaflet that can have another molecule
(e.g. cholesterol) in the tail region.
- add refnx.reflect.possibly_create_scatterer.
- remove refnx._lib._qmc, changing to scipy.stats.qmc.
- transition vendored ptemcee to use np.random.Generator.
- convert use of scipy.integrate.quadrature to scipy.integrate.quad.
- Appropriate unit conversion when loading ORSO data (1/nm to 1/angstrom).

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- rudimentary exporter of a Structure to an ORSO model language file,
`Structure.to_orso()`. Can only export Structures made of Slabs at the
moment.
- fixed bug in SpatzNexus.chod(). Repeat calls to this method would result
in increasing values because an array value wasn't being dereferenced.
- Fix several DeprecationWarnings emitted during tests.
- Fix numpy deprecation warning for `Parameters.__array__`. This method is
used to quickly extract the parameter set into a numpy array. This magic
method now requires the copy and dtype keywords, which we ignore in our
implementation.

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- Improve documentation for resolution smearing options in ReflectModel.
- Added refnx.reflect.create_occupancy, a helper function for creating occupancy
(volume fraction) profiles.
- Added codesigning for macOS thanks to the
International Scattering Association (ISA). This means that the refnx app
open a lot more easily on macOS, as it's not stopped by Gatekeeper.

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- added vectorised reflectivity calculator,
`refnx.reflect._creflect.abeles_vectorised`. This is mainly of use for
external programs, it's not used internally yet.
- Fix Parameter constraints that themselves depended on Parameters constrained
with functions.