Refnx

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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.

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- Fix bug in ReflectModelTL when numpy2 is installed.
- Added an example of incoherent summing in the documentation.
- Added `reflect.FunctionalForm` for Functional profiles. This was previously
only present in refnx-models.

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- Stop repeat append of a Parameter to Objective.model.parameters when the
Objective uses lnsigma, alpha, or auxiliary_params
- reenable pymc tests and update so that it works with pymc5
- add pymc/emcee/dynesty example to show how to use all three packages to
sample a posterior.
- add jax function for smeared reflectivity.
- optimisation of ReflectModelTL.
- add refnx.reflect._cyreflect.abeles_vectorised, a vectorised reflectivity
calculator with optional parallelisation

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- build against numpy=2
- update gh runners

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- Store the fname as a PurePath in Data1D. This is because pickled datafiles
from one OS may not be unpickleable on another OS. e.g. Posix can't unpickle
WindowsPath and vice versa.
- modified `util.general.neutron_transmission` to be able to select which cross
sections are used for transmission calculation.
- We revised the ReflectReduce.write_offspecular to output an ascii file with
four columns, qz,qx,m_ref, m_ref_err.
- ReflectModelTL added. Carries out reflectivity for wavelength dependent
scattering length density profiles.