python LSP: strip down Python kernel LSP to basic features

[austin3dickey]

• DataFrame/Series column completions (df['col'])
• Dictionary key completions (live objects)
• os.environ variable completions
• IPython magic command completions
• Runtime-aware hover (object previews)
• Live object type information

This could mean removing the Jedi dependency.

[seeM]

Some thoughts:

1. Might be worth looking into replacing Jedi with tree sitter. We use pretty low level functionality from Jedi, basically just the AST for a lot of these, and no Jedi for magic completions
2. pygls has been a pretty solid Python LSP framework for us, so seems fine to continue with it. We're on an old version though I think
3. Support notebooks from the start
4. Seems like a good candidate to vibe code a prototype 🤖

[austin3dickey]

Going to bump this issue to 2026.01.0 because it's not quite done yet. But it's mostly done in 2025.12.0. Just some completions are duplicated, and we want to refactor the code to remove tech debt anyway.