Prepare for 2.4.0 release

[vlad-perevezentsev]

The PR updates __version__ and CHANGELOG.md to publish the new 2.4.0 release

[jharlow-intel]

Version bump and changelog look right and match the 2.3.0 release PR (#349); the new #382 and #389 entries match the merged code.

[antonwolfy]

I checked the version bump and the final 2.4.0 changelog against the code merged in this cycle. The version bump looks good. My comments are inline, plus two on lines outside the diff:

• CHANGELOG.md:11 (Python 3.15): mkl-service has no cp315 wheel and no sdist on PyPI yet (2.8.0 ships cp310–cp314 only). So on 3.15, pip install "mkl_fft[scipy_interface]" and pip install "mkl_fft[test]" fail to resolve. Both clang workflows already leave out 3.15 for this reason (see the TODO there). I'd add a short note about this to the entry.
• CHANGELOG.md:27-28 (gh-364, gh-365): both only silence Coverity reports and change nothing at runtime. One declares cdef int f_ndim, the other adds (void)status for an assert that is compiled out under -DNDEBUG. Under "Fixed" they read as if 2.3.x had real bugs in _allocate_result and __create_descriptor_1d. I'd drop them, same as the gh-374 entry.

[antonwolfy]

Thanks, the refined entries address my comments. The new wording matches the merged code.