[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>

devscripts/changelog_override.json

@@ -196,5 +196,15 @@
         "when": "b31b81d85f00601710d4fac590c3e4efb4133283",
         "short": "[ci] Rerun failed tests (#11143)",
         "authors": ["Grub4K"]
+    },
+    {
+        "action": "add",
+        "when": "a886cf3e900f4a2ec00af705f883539269545609",
+        "short": "[priority] **py2exe is no longer supported**\nThis release's `yt-dlp_min.exe` will be the last, and it's actually a PyInstaller-bundled executable so that yt-dlp users updating their py2exe build with `-U` will be automatically migrated. [Read more](https://github.com/yt-dlp/yt-dlp/issues/10087)"
+    },
+    {
+        "action": "add",
+        "when": "a886cf3e900f4a2ec00af705f883539269545609",
+        "short": "[priority] **Following this release, yt-dlp's Python dependencies *must* be installed using the `default` group**\nIf you're installing yt-dlp with pip/pipx or requiring yt-dlp in your own Python project, you'll need to specify `yt-dlp[default]` if you want to also install yt-dlp's optional dependencies (which were previously included by default). [Read more](https://github.com/yt-dlp/yt-dlp/pull/11255)"
     }
 ]