[MLIR][Python] enable type stub auto-generation (#155741)

This PR turns on automatic type stub generation (rather than relying on
hand-written/updated stubs). It uses nanobind's [stubgen
facility](https://nanobind.readthedocs.io/en/latest/typing.html#stub-generation).
If you would like to enable this functionality you can add
`GENERATE_TYPE_STUBS` to `declare_mlir_python_extension` .

GitOrigin-RevId: 22c2e15408553b2c172d407a8ee417adc2a93757