box: fix SIGSEGV on unaligned access to `struct applier`

All structures with a non-default alignment (set by `alignas()`) must be
allocated by `aligned_alloc()`, otherwise an access to such a structure
member fill crash, e.g. if compiled with AVX-512 support.

See also commit a60ec82d4f07 ("box: fix SIGSEGV on unaligned access to a
struct with extended alignment").

Closes #10699

NO_DOC=bugfix
NO_CHANGELOG=minor
NO_TEST=tested by debug_asan_clang workflow

(cherry picked from commit bf091358806ed17bf44efd2cf382a43c0ba49fe0)