fix issues with set_workers

[vtavana]

resolves #177

[Copilot]

Pull Request Overview

This PR fixes issues with the set_workers functionality in the SciPy interface of mkl_fft, aligning the default workers value with the maximum number of threads provided by MKL instead of the CPU count. Key changes include updating tests to use mkl.get_max_threads(), refactoring the logic in _workers_to_num_threads, and updating documentation and changelog accordingly.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
mkl_fft/tests/third_party/scipy/test_multithreading.py	Updated tests to use mkl.get_max_threads() instead of os.cpu_count() and adjusted expected default values.
mkl_fft/interfaces/_scipy_fft.py	Refactored workers handling and error messaging to rely on MKL thread counts.
mkl_fft/interfaces/README.md	Updated documentation to reflect the new default behavior for workers.
CHANGELOG.md	Documented the fixes to the set_workers functionality.

Comments suppressed due to low confidence (2)

mkl_fft/tests/third_party/scipy/test_multithreading.py:56

• [nitpick] The slow test marker is currently commented out. Confirm that disabling this test is intentional, and if not, consider re-enabling it with proper configuration to ensure full test coverage.

# @pytest.mark.slow

mkl_fft/interfaces/_scipy_fft.py:103

• [nitpick] Replacing os.cpu_count() with mkl.get_max_threads() ensures consistency with the default worker behavior, but verify that this approach aligns with expected performance and behavior on systems where the two values might differ.

    # SciPy uses os.cpu_count()