Add Hermitian FFT to scipy interface

[vtavana]

Add Hermitian FFT to scipy interface

[Copilot]

Pull Request Overview

This PR adds support for Hermitian FFT functions to the Scipy interface in mkl_fft. Key changes include:

• Adding implementations for the Hermitian FFT functions (hfft, ihfft, hfft2, ihfft2, hfftn, ihfftn) in the core interface.
• Updating test files (test_multithreading.py and test_basic.py) to incorporate and validate the new Hermitian FFT functionality.
• Modifying function signatures (making the plan parameter keyword‐only) and updating helper modules (_scipy_fft.py, _numpy_fft.py, _fft_utils.py) to support the new features.

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mkl_fft/tests/third_party/scipy/test_multithreading.py	Added Hermitian FFT functions in the multithreading tests.
mkl_fft/tests/third_party/scipy/test_basic.py	Unskipped and updated tests to include Hermitian FFT functions and updated expected behaviors.
mkl_fft/_scipy_fft.py	Extended the Scipy FFT interface by adding new Hermitian FFT functions and altering function signatures (plan parameter as keyword-only).
mkl_fft/_numpy_fft.py	Updated Hermitian FFT implementations and adjusted imports to include _swap_direction.
mkl_fft/_fft_utils.py	Added the _swap_direction helper to the module’s public API.

Files not reviewed (1)

• CHANGES.rst: Language not supported

[ndgrigorian]

LGTM