MAINT: Fix packaging metadata and align the dependency files

[bashtage]

Correct the metadata that is published to PyPI, and make pyproject.toml,
requirements*.txt and meson.build agree for the 7.1 release. No minimum
version rises, except that statsmodels 0.13.1 replaces 0.13.0.

pyproject.toml

• Fix the dev extra, which listed "pandas-stubsl". That name does not exist
  on PyPI, so "pip install linearmodels[dev]" failed.
• Add Python 3.14 and 3.15 to the classifiers. requires-python is unchanged.
• Require statsmodels>=0.13.1. 0.13.0 has no wheel for Python 3.10, and
  0.13.1 is the version that the CI job for the minimum versions tests.
• Add packaging to the dependencies. linearmodels.compat imports it at run
  time, and it only arrived through statsmodels.
• Use pytest>=9,<10 in the test and dev extras, as requirements-test.txt
  already does, and set minversion to 9.0. pyproject.toml is installed with
  the package, so this also applies to linearmodels.test(), which now stops
  with an error that asks for pytest 9.0 when it is run with pytest 8.
• Use --strict-markers in addopts, and drop the filterwarnings entry for
  the warning that --strict raised in pytest 8. In pytest 9, --strict is no
  longer an alias: it enables strict_config, strict_markers, strict_xfail
  and strict_parametrization_ids. Markers and xfail are still checked
  (xfail_strict is set), but unknown configuration options and duplicate
  parametrization ids no longer fail the tests.
• Clean up the doc extra. setuptools_scm is >=9.2.0,<10 as in the build
  system. Remove oldest-supported-numpy, patsy, which linearmodels does not
  use, and the stale pandas~=2.3.3 pin. Remove the second entries for ipython,
  sphinx-immaterial and sphinx-autodoc-typehints.
• Remove [tool.setuptools_scm]. It was copied from arch and named
  arch/_version.py. Nothing reads it: meson.build gets the version from
  linearmodels/_build/git_version.py, which calls setuptools_scm.get_version
  with explicit arguments, and that function does not read pyproject.toml.
  git_version.py returns the same version with and without the table.
• Turn the mypy tables for linearmodels.conftest and linearmodels._version
  into [[tool.mypy.overrides]]. pyproject.toml ignores them as written, since
  they use INI syntax. Change the module of the override for the tests from
  "mypy-linearmodels.tests.", which is not a valid pattern, to
  "linearmodels.tests.*". mypy reports the same 65 errors in the same 10 files
  as before.

Other files

• requirements.txt: match pyproject.toml, with formulaic>=1.2.1 (not 1.0.2),
  statsmodels>=0.13.1 and packaging. Remove wrapt!=2.0.0rc3. It excluded a
  release candidate of wrapt, which formulaic depends on and linearmodels
  does not import, in a commit that gave no reason (5497ece). wrapt
  2.0.0rc4 and 2.0.0 have been released since.
• meson.build, requirements-dev.txt, the dev extra: use the Cython minimum of
  the build system, 3.0.13, instead of 3.0.10. There is no Cython 3.0.13:
  3.0.12 is followed by 3.1.0. In practice, this means Cython 3.1 or later.
• requirements-dev.txt: use setuptools_scm>=9.2.0,<10, as the build system
  does (it had <9), and pytest>=9,<10.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.58%. Comparing base (208845b) to head (3f82f71).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #757   +/-   ##
=======================================
  Coverage   99.58%   99.58%           
=======================================
  Files         110      110           
  Lines       20328    20328           
  Branches     1600     1600           
=======================================
  Hits        20244    20244           
  Misses         31       31           
  Partials       53       53           

Flag	Coverage Δ
adder	99.57% <ø> (ø)
subtractor	99.57% <ø> (ø)

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