Add MKLMemory class to expose MKL allocated memory via Python buffer protocol

[ndgrigorian]

This PR proposes the introduction of _mkl_memory.pyx, which implements an MKLMemory class that exposes memory allocated via mkl_malloc and mkl_calloc to Python via the buffer protocol

The class uses an atomic counter incremented as __getbuffer__ and __releasebuffer__ are called to track the views on the buffer to permit use of mkl_realloc in the object (via realloc method). This concept was adapted from the PEP which revised the buffer protocol which proposed this kind of approach to tracking views on a buffer

Closes#18

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a new MKLMemory Cython extension type backed by MKL’s allocator, exposes it from the top-level mkl package, and introduces tests/build changes to support C11 atomics and nogil MKL calls.

Changes:

• Introduce mkl._mkl_memory with MKLMemory (allocation, buffer protocol, pickling, realloc).
• Add pytest coverage for allocation, buffer protocol, and pickling behavior.
• Update MKL C-API declarations/build to support nogil calls and C11 atomics (plus MSVC flag).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
mkl/tests/test_mkl_memory.py	Adds tests for MKLMemory creation, buffer protocol, and pickling behavior.
mkl/_py_mkl_service.pyx	Releases the GIL around MKL buffer-free calls.
mkl/_mkl_service.pxd	Marks MKL externs as nogil and adds malloc/calloc/realloc/free declarations.
mkl/_mkl_memory.pyx	Adds the new MKLMemory Cython extension implementing allocation + buffer protocol + pickling.
mkl/init.py	Exposes MKLMemory at the package top level.
meson.build	Enables C11, adds MSVC atomics flag, and builds the new _mkl_memory extension.