Remove dependency to pkg_resources

[ikkoham]

Summary

Since pkg_resources.declare_namespace has been deprecated, our CI is failed.
I removed the dependency to pkg_resources.

Details and comments

CI message

==============================
Failed 1 tests - output below:
==============================

test.python.test_version.TestVersion.test_qiskit_version
--------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/Users/runner/work/1/s/test/python/test_version.py", line 25, in test_qiskit_version
    self.assertEqual(__version__, __qiskit_version__["qiskit-terra"])
                                  ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^

      File "/Users/runner/work/1/s/qiskit/version.py", line 168, in __getitem__
    self._load_versions()

      File "/Users/runner/work/1/s/qiskit/version.py", line 104, in _load_versions
    import pkg_resources

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 3257, in <module>
    @_call_aside
     ^^^^^^^^^^^

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 3232, in _call_aside
    f(*args, **kwargs)

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 3283, in _initialize_master_working_set
    tuple(dist.activate(replace=False) for dist in working_set)

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 3283, in <genexpr>
    tuple(dist.activate(replace=False) for dist in working_set)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 2804, in activate
    declare_namespace(pkg)

      File "/Users/runner/work/1/s/test-job/lib/python3.11/site-packages/pkg_resources/__init__.py", line 2298, in declare_namespace
    warnings.warn(msg, DeprecationWarning, stacklevel=2)

    DeprecationWarning: Deprecated call to `pkg_resources.declare_namespace('mpl_toolkits')`.
Implementing implicit namespace packages (as specified in PEP 420) is preferred to `pkg_resources.declare_namespace`. See https://setuptools.pypa.io/en/latest/references/keywords.html#keyword-namespace-packages

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[ikkoham]

hmm importlib.metadata is >= Python 3.8

[coveralls]

Pull Request Test Coverage Report for Build 4302012175

• 5 of 6 (83.33%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 85.342%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/version.py	5	6	83.33%

Files with Coverage Reduction	New Missed Lines	%
src/sabre_swap/layer.rs	4	97.32%

Totals
Change from base Build 4296421416:	0.02%
Covered Lines:	67479
Relevant Lines:	79069

---

💛 - Coveralls

[ikkoham]

we have https://github.com/Qiskit/qiskit-terra/blob/main/requirements.txt#L19

[1ucian0]

Thanks for the quick reaction!

[mtreinish]

FWIW, I think we can probably do this as a module level import. The pkg_resources import was done at runtime because it was exceedingly slow. I don't expect importlib.metadata to have this issue (but it would be worth checking to confirm) and I think it probably gets pulled in already via our plugin interfaces. That being said it doesn't actually matter in practice so it's not worth a follow up PR.

[ikkoham]

Thanks. I did not know the reason of lazy import here.