Options: adapt shots upper bound

[airwoodix]

Summary

The cloud portal now accepts shots settings up to 2000. This is not the case for direct-access resources, where the limit is 200.

This PR updates the shots upper bound for cloud resources. This requires having distinct options models for different resource types.

Details and comments

Qiskit BackendV2._default_options

The default options reported by BackendV2._default_options are now aligned with the actual defaults provided by the relevant model. Since BackendV2._default_options must be a classmethod, the options model is retrieved from the _ResourceBase type argument. An alternative would be to use a subclass hook, but this would be more invasive.

Documentation

Sphinx support for type variables is provided by the new development dependency sphinx-toolbox.

Autodoc's autoclass/autoproperty directives seem to assume that method return types are classes (!), thus the link to the _OptionsType type variable for the options property is not rendered and needs a nitpicky exception. The _ResourceBase type argument is properly linked.