Subdue some compiler warnings when compiling in debug mode

[anyzelman]

List of known warnings:

graphblas/src/transition/fuselets.cpp:341:30: warning: comparison of integer expressions of different signedness
graphblas/src/transition/fuselets.cpp:342:20: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:306:39: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:310:43: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:340:23: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:341:21: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:353:20: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/utils/unordered_memmove.hpp:354:20: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1036:25: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1037:11: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1082:25: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1083:11: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1118:25: warning: comparison of integer expressions of different signedness
graphblas/include/graphblas/reference/blas3.hpp:1119:11: warning: comparison of integer expressions of different signedness

Some new warnings that should likely be suppressed are the following:

graphblas/include/graphblas/reference/blas1.hpp:3744:9: warning: 'z_b[7]' may be used uninitialized in this function [-Wmaybe-uninitialized]
 3744 |         *( z_p + index ) = z_b[ k ];
      |         ^