deps: add missing dependencies in test group

[nazarpechka]

This PR adds missing dependencies to pyproject.toml test dependency group (used for local development).
Added dependencies:

• codespell - required to run make spell_check and make spell_fix scripts
• pytest-watcher - required to run make test_watch
• greenlet - without it, make test fails with error below. It was previously added in Dependencies: Add greenlet package to test dependency group #161, but lost at some point.

ValueError: the greenlet library is required to use this function. No module named 'greenlet'

[averikitsch]

Instead of installing greenlet directly, I believe we can update sqlalchemy to SQLAlchemy[asyncio].

[nazarpechka]

@averikitsch Thanks, updated to sqlalchemy[asyncio].
This is a library dependency, so we will force all users to also install greenlet. This should not be a problem though, as using AsyncPgVectorStore needs it anyway.