Add parametrized tests across emulators that init arguments are captured

[sgreenbury]

As identified in #918, current tests for MLP (and other emulators) do not look at whether passed arguments at init are stored in the instance.

It would be good to have a parameterized test across emulators that is able to:

• inspect the emulators arguments
• check what defaults are present
• check the type hint
• change the value to a different valid value
• instantiate the emulator
• test each of the fields have been initialized to that passed

There might be useful connection to kw_only in dataclass.

Originally posted by @EdwinB12 in #918 (review)