build: Require Python 3.8+

* For the requires-python metadata, require Python 3.8+ as all CPython versions
  up through Python 3.7 are now EOL.
   - c.f. https://packaging.python.org/en/latest/specifications/core-metadata/#requires-python

┌───────┬────────────┬─────────┬────────────────┬────────────┬────────────┐
│ cycle │  release   │ latest  │ latest release │  support   │    eol     │
├───────┼────────────┼─────────┼────────────────┼────────────┼────────────┤
│ 3.12  │ 2023-10-02 │ 3.12.2  │   2024-02-06   │ 2025-04-02 │ 2028-10-31 │
│ 3.11  │ 2022-10-24 │ 3.11.8  │   2024-02-06   │ 2024-04-01 │ 2027-10-31 │
│ 3.10  │ 2021-10-04 │ 3.10.13 │   2023-08-24   │ 2023-04-05 │ 2026-10-31 │
│ 3.9   │ 2020-10-05 │ 3.9.18  │   2023-08-24   │ 2022-05-17 │ 2025-10-31 │
│ 3.8   │ 2019-10-14 │ 3.8.18  │   2023-08-24   │ 2021-05-03 │ 2024-10-31 │
│ 3.7   │ 2018-06-26 │ 3.7.17  │   2023-06-05   │ 2020-06-27 │ 2023-06-27 │
│ 3.6   │ 2016-12-22 │ 3.6.15  │   2021-09-03   │ 2018-12-24 │ 2021-12-23 │
│ 3.5   │ 2015-09-12 │ 3.5.10  │   2020-09-05   │   False    │ 2020-09-30 │
│ 3.4   │ 2014-03-15 │ 3.4.10  │   2019-03-18   │   False    │ 2019-03-18 │
│ 3.3   │ 2012-09-29 │ 3.3.7   │   2017-09-19   │   False    │ 2017-09-29 │
│ 3.2   │ 2011-02-20 │ 3.2.6   │   2014-10-12   │   False    │ 2016-02-20 │
│ 3.1   │ 2009-06-26 │ 3.1.5   │   2012-04-06   │   False    │ 2012-04-09 │
│ 3.0   │ 2008-12-03 │ 3.0.1   │   2009-02-12   │   False    │ 2009-06-27 │
│ 2.7   │ 2010-07-03 │ 2.7.18  │   2020-04-19   │   False    │ 2020-01-01 │
│ 2.6   │ 2008-10-01 │ 2.6.9   │   2013-10-29   │   False    │ 2013-10-29 │
└───────┴────────────┴─────────┴────────────────┴────────────┴────────────┘

* Retain upper bound on CPython as the dependency on the CPython AST is brittle given
  large changes from CPython.

setup.py

@@ -9,8 +9,7 @@
                  long_description=long_description,
                  long_description_content_type="text/markdown",
                  packages=setuptools.find_packages(exclude=['tests']),
-                 python_requires=('>=2.7, '
-                                  '!=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*, <3.13'),
+                 python_requires=('>=3.8, <3.13'),
                  install_requires=['lark'],
                  extras_require={'test': ['flake8', 'pytest', 'pytest-cov']},
                  package_data={'qastle': ['syntax.lark']},