Dust off and update V8 to 12.2

[bpcreech]

Lots of changes here. From HISTORY.md:

• Update V8 to 12.2
• Drop Python 2 support
• Fix small Python 3.12 issue and add testing for Python 3.9-3.12
• Add aarch64 support for Mac and Linux
• Revamp DLL loading to be compliant with Python 3.9-style resource loading. This may present a small breaking change for advanced usage; the EXTENSION_PATH and EXTENSION_NAME module variables, and MiniRacer.v8_flags and MiniRacer.ext class variable have all been removed.
• Add support for the ECMAScript internalization API and use fast startup snapshots
• Switch from setuptools to Hatch
• Switch from tox to Hatch
• Switch from flake8 and isort to Hatch's wrapper of Ruff
• Switch from Sphinx to mkdocs (and hatch-mkdocs)
• Switch from reStructuredText to Markdown
• Switch from unittest to pytest
• Add ARCHITECTURE.md and lots of code comments

A lot of these changes are just trying to update the package to "Python ecosystem 2024" (i.e., Hatch and friends).

I ended up making these updates in interleaved order in a way that's not useful for incremental review, so I just squashed to one commit. I could split this back out into logical changes if that's useful, but it will take some hours. :)

I'm not sure if this should be a PR, or if we should move the official repo, or what; depends on what the ex-Sqreen folks think!

[bpcreech]

BTW docs can be previewed at https://bpcreech.com/PyMiniRacer

[bpcreech]

Update: after discussion with @nizox and @aviat we decided to fork PyMiniRacer into https://github.com/bpcreech/PyMiniRacer for its continued life.

This PR (and more) are landed there.