Python-graphblas

* (47) bug fix: OpenMP atomics require seq_cst on the ARM.
Revised GB_atomics.h accordingly, and added them for all
architectures (caught by Gabor Szarnyas).

This version will appear as the ACM Collected Algorithm 10xx for this paper: https://dl.acm.org/doi/10.1145/3577195 .

* debug: turned on in GrB_Matrix_removeElement by mistake.

* minor change to build system: for SuiteSparse v7.0.0
* deprecation notice: in GraphBLAS v8.0.0, the ability to set the
of threads, and chunk size, in the descriptor will be removed.
It still appears in v7.x, but will be replaced by a Context object
in v8.0.0.

This version appears in SuiteSparse v7.0.0 as well.

* global free pool: disabled. Benefit for single-thread user applications
was modest, and it causes too much contention in a critical section
when the user application is multi-threaded.
* GrB_mxm: revised task creation heuristics for sparse-times-sparse for
better performance. "chunk" and "very_costly" had been tuned in v7.3.x
for sparse-times-dense but this slowed down sparse-times-sparse. The
new heuristic keeps the chunk & very_costly parameters for
sparse-times-dense but restores the prior values for
sparse-times-sparse from v7.2.0 (Aug 8, 2022). See
Source/GB_AxB_saxpy3_slice_balanced.c.

* added non-va_arg methods: va_arg-based GxB_get/set methods are ANSI C11
but cause issues for cffi in Python. As a temporary workaround, new
methods have been added that do not use va_arg. The existing
GxB_get/set methods are not changed. The new methods are not in the
user guide, since all of the GxB_get/set methods will be superceded
with GrB_get/set in the v2.1 C API. At that point, all GxB_get/set
methods will become historical (kept, not deprecated, but removed from
the user guide).

* minor change to build system
* stdatomic.h: using include <stdatomic.h> and atomic_compare_exchange_weak
instead of GCC/clang/icx __atomic_* variants.
Added -latomic if required.
* chunk factor for C=A*B (saxpy3 method): revised for non-builtin-semirings