Make V2 primitive input container classes private

[chriseclectic]

Summary

Make the V2 primitives input container and pubs classes private and removes them from public API Docs

Details and comments

This removes the EstimatorPub, SamplerPub, BindingsArray, ObservablesArray classes from API docs to make them internal and not subject to qiskits deprecation policies for public classes. This is because we have not had sufficient time to fully finalize these classes before the 1.0 release and anticipate making possibly breaking changes to them in future qiskit releases.

Note that we still intend for the <class>Like type hints to be in the API docs, though im not entirely sure how to get these to build and render in sphinx with propert doc strings and without unrolling all the composite type hints.

[qiskit-bot]

One or more of the the following people are requested to review this:

• @Qiskit/terra-core
• @ajavadia
• @ikkoham
• @levbishop
• @t-imamichi

[coveralls]

Pull Request Test Coverage Report for Build 7731026313

• -3 of 48 (93.75%) changed or added relevant lines in 8 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.02%) to 89.606%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/primitives/containers/observables_array.py	27	30	90.0%

Files with Coverage Reduction	New Missed Lines	%
qiskit/primitives/statevector_estimator.py	1	94.55%
crates/qasm2/src/lex.rs	4	91.94%

Totals
Change from base Build 7729918317:	0.02%
Covered Lines:	59357
Relevant Lines:	66242

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💛 - Coveralls

[t-imamichi]

Don't we need to rename classes with prefix "_", e.g., BindingsArray → _BindingsArray?

[ikkoham]

I don't think the definition of private in Qiskit is clear. Is it private if it is not in __init__.py or if it starts with _? @mtreinish
If the former, I approve.

[mtreinish]

From qiskit 1.0 moving forward we're being more explicit about what are public stable interface is. We've documented the stable public interface for qiskit as being anything documented: https://docs.quantum.ibm.com/start/install#qiskit-versioning (it's annoyingly under the "release schedule" section and I can't directly link to it). So ensuring that we're not re-exporting it from __init__.py and making sure it's not documented is sufficient to have the the classes treated as private. That being said prepending them with _ makes the classes explicitly private and will likely reduce confusion around them, even if it's not strictly required.

[ihincks]

I have a slight preference not to rename them to start with _ because about 4 other repos would need to be changed to accommodate, both now, and when we make them public. Maybe I should be more concerned about user confusion, but since these things are silently created inside of the primitive and not returned, I can't see how it would be common-place.

[ihincks]

LGTM, but I would like to brainstorm a bit more improving the visibility of the *Like union types in our api docs.

[ihincks]

Approving because concerns in my previous comment can be their own PR.