Improve handling of circuit execution providers

This change improves several aspects about the way `ExperimentData`
works with "providers." Here "provider" is generalized beyond
`qiskit.providers.Provider` to any object which can provide a `Job`-like
object with data about an experiment's circuit execution. This
generalization is needed because `qiskit-ibm-runtime`, the main provider
that Experiments integrates with, does not use the `Provider` class, so

* Replace references to `qiskit.providers.Provider` and
  `qiskit.providers.Job` with  custom interface definitions using
`typing.Protocol`. The new interfaces document the API Experiments needs
for working with these objects.
* Improve type hints and type checking related to providers, jobs, and
  results, using the new protocol classes.
* Infer `IBMExperimentService` authentication parameters from a
  `qiskit_ibm_runtime.QiskitRuntimeService` instance in the same way
that the inference used to work with `qiskit_ibm_provider.IBMProvider`.
* Delay inferring an `IBMExperimentService` from a backend or provider
  until `ExperimentData` tries to communicate with the experiment
service. With the fix to infer the authentication parameters from
`QiskitRuntimeService`, this delay is needed to avoid breaking existing
code that creates an `ExperimentData` instance and then tries to set a
custom experiment service for it, relying on the fact that inferrence
did not work for `QiskitRuntimeService`, since setting the service on
`ExperimentData` after it has already been set once raises an exception.
* Remove dead code, both helper functions that are not called anywhere
  in the repository and code paths only relevant to qiskit-ibm-provider,
like references to `time_per_step()`. Since `qiskit-ibm-provider` has
long been deprecated and unsupported by IBM Quantum, removing support
for it is not treated as a breaking change.
* Handle some optional data types better (like result objects that might
  have a `metadata` attribute).

qiskit_experiments/framework/__init__.py

@@ -93,6 +93,12 @@
     ExperimentDecoder
     ArtifactData
     FigureData
+    Provider
+    BaseProvider
+    IBMProvider
+    Job
+    BaseJob
+    ExtendedJob
 
 .. _composite-experiment:
 
@@ -154,4 +160,5 @@
     CompositeAnalysis,
 )
 from .json import ExperimentEncoder, ExperimentDecoder
+from .provider_interfaces import BaseJob, BaseProvider, ExtendedJob, IBMProvider, Job, Provider
 from .restless_mixin import RestlessMixin