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

Why? https://nanobind.readthedocs.io/en/latest/why.html says it better
than I can, but my primary motivation for this change is to improve MLIR
IR construction time from JAX.

For a complicated Google-internal LLM model in JAX, this change improves
the MLIR
lowering time by around 5s (out of around 30s), which is a significant
speedup for simply switching binding frameworks.

To a large extent, this is a mechanical change, for instance changing
`pybind11::`
to `nanobind::`.

Notes:
* this PR needs Nanobind 2.4.0, because it needs a bug fix
(https://github.com/wjakob/nanobind/pull/806) that landed in that
release.
* this PR does not port the in-tree dialect extension modules. They can
be ported in a future PR.
* I removed the py::sibling() annotations from def_static and def_class
in `PybindAdapters.h`. These ask pybind11 to try to form an overload
with an existing method, but it's not possible to form mixed
pybind11/nanobind overloads this ways and the parent class is now
defined in nanobind. Better solutions may be possible here.
* nanobind does not contain an exact equivalent of pybind11's buffer
protocol support. It was not hard to add a nanobind implementation of a
similar API.
* nanobind is pickier about casting to std::vector<bool>, expecting that
the input is a sequence of bool types, not truthy values. In a couple of
places I added code to support truthy values during casting.
* nanobind distinguishes bytes (`nb::bytes`) from strings (e.g.,
`std::string`). This required nb::bytes overloads in a few places.

mlir/python/CMakeLists.txt

@@ -448,6 +448,7 @@ declare_mlir_python_extension(MLIRPythonExtension.Core
   MODULE_NAME _mlir
   ADD_TO_PARENT MLIRPythonSources.Core
   ROOT_DIR "${PYTHON_SOURCE_DIR}"
+  PYTHON_BINDINGS_LIBRARY nanobind
   SOURCES
     MainModule.cpp
     IRAffine.cpp
@@ -463,7 +464,7 @@ declare_mlir_python_extension(MLIRPythonExtension.Core
     Globals.h
     IRModule.h
     Pass.h
-    PybindUtils.h
+    NanobindUtils.h
     Rewrite.h
   PRIVATE_LINK_LIBS
     LLVMSupport

mlir/python/requirements.txt

@@ -1,4 +1,4 @@
-nanobind>=2.0, <3.0
+nanobind>=2.4, <3.0
 numpy>=1.19.5, <=2.1.2
 pybind11>=2.10.0, <=2.13.6
 PyYAML>=5.4.0, <=6.0.1