Validate Python bindings argument config

What

Add tests to validate that the arguments on Python bindings for functions/methods are configured correctly

Why

It's easy to make a typo and get them wrong, and fixing it can be an API breaking change.

ACs

Tests for all Python bindings of functions, to ensure that

• All arguments can be used as both positional and keyword (py::args are added).
• The arguments have the correct name, mirroring the C++ argument name.
• None is disallowed (i.e. .none(false)) as appropriate for pointer-like types, and lists of pointer-like types.

Original issue for posterity

What

Decide on Python bindings positional vs. keyword argument policy, and then conform and test them.

Why

If py::arg is not used to document constructor/method arguments, then pybind will require arguments to be positional.

However, this means the signature docstrings (also shown in some pybind exceptions) are less informative, e.g. arguments are named arg0 etc in the docs.

Using py::arg or py::arg_v to name the arguments gives better docs, but then by default also allows the arguments to be provided as keyword arguments.

Locate the C++ Python binding definitions and the existing tests covering them, then run the relevant test suite to understand current coverage. Add checks for argument names, positional and keyword use, and appropriate None handling across all function bindings; done means the stated acceptance criteria pass for every binding.