Improve Ami430 safety and type annotations

docs/changes/newsfragments/8679.breaking

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+The field units of an ``AMIModel430`` can no longer be changed while it is part of an
+``AMIModel4303D``, and doing so now raises a ``RuntimeError``. The set point and field limit of
+the 3D driver are in the field units of the magnets, so changing them silently changed their
+meaning by a factor of 10. Set the field units before creating the 3D driver, or close the 3D
+driver first.
+
+The coordinate vectors of ``AMIModel4303D`` (``cartesian``, ``spherical``, ``cylindrical`` and
+their ``*_measured`` versions) now return a named tuple (``CartesianVector``,
+``SphericalVector`` or ``CylindricalVector`` from ``qcodes.math_utils``) instead of a list, so
+the components can also be accessed by name, e.g. ``cartesian_measured().z``. Code that compares
+the result to a list, or modifies it, needs updating. Setting these parameters still accepts
+lists, tuples and numpy arrays.

docs/changes/newsfragments/8679.improved_driver

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+The field parameters of ``AMIModel4303D``, such as ``cartesian``, ``x`` and ``field_measured``,
+now use the field units of the individual magnets, tesla or kilogauss, instead of always
+reporting tesla. A warning is logged if the magnets use different field units. Also removed the
+placeholder unit ``tuple?`` of ``AMIModel4303D.spherical`` and ``cylindrical``, whose components
+have different units, which are now described in their docstrings. Closing an
+``AMIModel4303D`` now detaches its magnets, so ``set_field``, ``zero`` and changing the units of
+a magnet that is still open no longer fail.

docs/changes/newsfragments/8679.new

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+Added the named tuples ``CartesianVector`` (``x``, ``y``, ``z``), ``SphericalVector``
+(``field``, ``theta``, ``phi``) and ``CylindricalVector`` (``rho``, ``phi``, ``z``) to
+``qcodes.math_utils``, for the components of a field vector in a given coordinate system.