[cleanup] Misc (#11216)

- Add Python 3.13 to CI, finalize 3.13 support
- Remove Python 3.8 from CI in preparation for removing 3.8 support
- Document that PyPy3.8 and PyPy3.9 are no longer supported
- Usual documentation fixes and code cleanup

Closes #8248, Closes #11146, Closes #11149, Closes #11211
Authored by: Grub4K, grqz, DTrombett, KarboniteKream, bashonly, mikkovedru, seproDev

Co-authored-by: N/Ame <173015200+grqz@users.noreply.github.com>
Co-authored-by: DTrombett <d@trombett.org>
Co-authored-by: =?UTF-8?q?Klemen=20Ko=C5=A1ir?= <klemen.kosir@kream.io>
Co-authored-by: bashonly <88596187+bashonly@users.noreply.github.com>
Co-authored-by: Mikko Vedru <mikko.vedru@gmail.com>
Co-authored-by: sepro <sepro@sepr0.com>

pyproject.toml

@@ -34,6 +34,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: Implementation",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",
@@ -169,13 +170,11 @@ run-cov = "echo Code coverage not implemented && exit 1"
 
 [[tool.hatch.envs.hatch-test.matrix]]
 python = [
-    "3.8",
     "3.9",
     "3.10",
     "3.11",
     "3.12",
-    "pypy3.8",
-    "pypy3.9",
+    "3.13",
     "pypy3.10",
 ]