Previously, we used std::array<std::initializer_list, 27> to store a multi-dimensional array. However, initializer_list objects only hold pointers to their underlying data, not the data itself. When initialized with brace-enclosed lists like {0,1,2,3}, the temporary arrays created by these literals are destroyed after the initialization expression completes, leaving the initializer_list objects pointing to deallocated memory.

This caused AddressSanitizer to detect stack-use-after-scope errors when getint() attempted to iterate over the initializer_list contents:

==2085499==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7f5fe9803580 at pc 0x55d851bea586 bp 0x7ffc9816a5b0 sp 0x7ffc9816a5a8
READ of size 4 at 0x7f5fe9803580 thread T0
    #0 0x55d851bea585 in getint(std::initializer_list<int>) /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/erasure-code/TestErasureCodeShec_arguments.cc:46:21
    #1 0x55d851bf0258 in int std::__invoke_impl<int, int (*&)(std::initializer_list<int>), std::initializer_list<int>&>(std::__invoke_other, int (*&)(std::initializer_list<int>), std::initializer_list<int>&) /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:61:14
...
Address 0x7f5fe9803580 is located in stack of thread T0 at offset 1408 in frame
    #0 0x55d851bdd07f in create_table_shec432() /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/erasure-code/TestErasureCodeShec_arguments.cc:52

Fix this by using std::array<std::array<int, 4>, 27> instead, which actually owns and stores the data rather than just pointing to it.

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