Move build system to meson-python

[ndgrigorian]

This PR proposes moving from setuptools to meson-python as the mkl_fft build system

meson-python is already used by NumPy and allows setup.py to be removed (with its logic moved into the meson.build script)

Also moves to mkl as dependency, with mkl-service only used as a dependency when using the scipy interface. If scipy is installed without mkl-service, the scipy interface won't be available

[Copilot]

Pull request overview

This PR migrates mkl_fft’s build backend from setuptools/setup.py to meson-python, moving extension/module build logic into meson.build and updating packaging/CI/conda recipes accordingly.

Changes:

• Switch PEP 517 build backend to mesonpy and drop setup.py-based build configuration.
• Add a Meson build definition that generates mklfft.c and builds/installs the _pydfti extension plus Python sources/tests.
• Update conda recipes and CI workflows to install Meson-based build dependencies and build via pip.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
setup.py	Removed legacy setuptools build script.
pyproject.toml	Switched build backend to mesonpy; adjusted formatter/lint tool config and removed setuptools-specific sections.
meson.build	New Meson build: MKL dependency discovery, source generation, Cython extension build, and install rules.
conda-recipe/meta.yaml	Add Meson build tooling to host requirements; remove setuptools.
conda-recipe/build.sh	Build/install via pip without setting MKLROOT.
conda-recipe/bld.bat	Build/install via pip without setting MKLROOT.
conda-recipe-cf/meta.yaml	Same as Intel recipe for conda-forge context.
conda-recipe-cf/build.sh	Build/install via pip instead of setup.py.
conda-recipe-cf/bld.bat	Build/install via pip instead of setup.py.
.github/workflows/build-with-standard-clang.yml	New CI job validating Meson-based builds with system clang.
.github/workflows/build-with-clang.yml	Update dependency installation to Meson-based toolchain (workflow still uses editable install later).
.github/workflows/build_pip.yml	Update dependency installation to Meson-based toolchain (workflow still uses editable install).
.flake8	Exclude new vendored helper script.
_vendored/README.md	Document additional vendored script origin.
_vendored/process_src_template.py	New vendored CLI for generating *.c from *.c.src.
_vendored/conv_template.py	Formatting/modernization changes to vendored tempita processor.

Comments suppressed due to low confidence (1)

.github/workflows/build_pip.yml:49

• This workflow still installs the package in editable mode (pip install -e ...), but build-with-standard-clang.yml explicitly notes that mkl_fft cannot be installed in editable mode. If editable installs are indeed unsupported with the meson-python backend, switch this workflow to a non-editable install (pip install .) and run tests from outside the repo checkout (e.g., cd ..) to ensure imports come from the installed wheel. If editable installs are intended to be supported, please drop/adjust the comment in build-with-standard-clang.yml and ensure meson-python minimum version is set accordingly.