[llvm] [mlir] [mlir python] Port Python core code to nanobind. (PR #118583)

[Stella Laurenzo via llvm-commits]

https://github.com/stellaraccident commented:

This all looks good to me. Thank you. 

Let's let the discourse conversation quiesce before landing, as discussed.

https://github.com/llvm/llvm-project/pull/118583