Explain better errors in EmulationConfig init

[HaroldErbin]

It would be helpful to give more information in errors thrown in EmulationConfig.__init__ such that it is easier to identify which particular argument fails.

For example, I am getting the following error:

  File "pulser/backend/config.py", line 276, in __init__
    raise TypeError(
TypeError: All entries in 'observables' must be instances of Observable. Instead, got instance of type <class 'str'>.

This requires a bit of work to identify the problematic observable. Changing the test on line 275 to:

if not isinstance(obs, Observable):
    raise TypeError(
        "All entries in 'observables' must be instances of "
        f"Observable. Instead, got instance of type {type(obs)}. "
        f"for observable {obs}."
    )

makes it much easier to identify the problem. Similar improvements can be done to other tests.

[HGSilveri]

I agree @HaroldErbin , I'm adding the issue to the next release. Thanks for taking the time!