Require `supports_sampler_stats=True` for all `BaseTrace`

[michaelosthege]

We don't have a backend that doesn't support it, and by requiring support we can simplify code.

[williambdean]

I'm interested in taking this issue in order to learn more about the backends submodule.

Could you give a little more details? Is this looking to remove the supports_sampler_stats attribute or just change default to True? I'm see that it is used in a few places.
Is the BaseTrace class still meant to be extended?

Thanks

[michaelosthege]

I think removing it right away should be fine.
My plan is to morph BaseTrace closer to mcbackend.Chain to make it easier to switch.
#6188 was part of that and so is #6192.

I you take on this issue it will help too!

[williambdean]

Great. Thanks for the context @michaelosthege

Okay. What I will do is remove all references to supports_sampler_stats and assume that is True. If there is any logic using supports_sampler_stats = False (ie raising Errors), I will remove those as well unless it depends on another condition.

Basically will follow the flow of logic where supports_sampler_stats = True

I will take a stab and open a PR

[michaelosthege]

sounds good, @wd60622 !
ping me for review when ready

[michaelosthege]

Closed by #6205 / 534b89b