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

[Stella Laurenzo via llvm-commits]

stellaraccident wrote:

Thanks @hawkinsp for the heavy lift and others for the pre-work to get such a big change sequence landed smoothly. Much appreciated. Happy new year.

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