Ml-dtypes

* Updates `ml_dtypes` for compatibility with the upcoming NumPy 2.0 release.
* Wheels are built against NumPy 2.0.0rc1.

* Updates `ml_dtypes` for compatibility with future NumPy 2.0 release.
* Wheels for the release candidate are built against NumPy 2.0.0b1.

* Fixed spurious invalid value warnings when casting between floating point
types on Mac ARM.
* Remove `pybind11` build requirement
* Update C++ sources for compatibility with NumPy 2.0

* Added support for `int4` casting to wider integers such as `int8`
* Added support to cast `np.float32` and `np.float64` into `int4`

* Dropped support for Python 3.8, following [NEP 29].
* Added support for Python 3.12.
* Removed deprecated name `ml_dtypes.float8_e4m3b11`; use `ml_dtypes.float8_e4m3b11fnuz` instead.

[NEP 29]: https://numpy.org/neps/nep-0029-deprecation_policy.html

New features:
* added new 4-bit integer types: `ml_dtypes.int4` and `ml_dtypes.uint4`

Deprecations:
* `ml_dtypes.float8_e4m3b11` has been renamed to `ml_dtypes.float8_e4m3b11fnuz` for more
consistency with other dtype names. The former name will still be available until
version 0.3.0, but will raise a deprecation warning.