chore: make Sphinx cookbook extension pip-installable

[lidavidm]

Fixes #2432.

[lidavidm]

Both of these should work:

pip install --dry-run 'git+https://github.com/lidavidm/arrow-adbc@gh-2432#subdirectory=docs/source/ext/illiterate_sphinx'
pip install --dry-run 'https://github.com/lidavidm/arrow-adbc/archive/gh-2432.zip#subdirectory=docs/source/ext/illiterate_sphinx'

The latter seems a bit faster.

[lidavidm]

After this, the main improvements I'd like to make are:

• Make sure Java/jshell works, too
• Work out some way to support showing expected stdout/stderr in the recipe (vs the current approach of using assertions). (The test harness would probably just validate the stdout/stderr as a whole, instead of trying to run the code line by line, but I think that's OK.)

[lidavidm]

I'm also reconsidering the name here, if anyone has better suggestions...

[paleolimbot]

Install worked great for me!

[lidavidm]

Thanks for checking! I think I'll rename the package just out of caution then merge it.