include/any.h: avoid using std::aligned_storage_t

include/any.h: avoid using std::aligned_storage_t

std::aligned_storage_t was deprecated in C++23, to be prepared for
it, let's use alignas for the same behavior. because we do not always
pass a power-of-2 number to `immobile_any`, while `alignas()` requires
an alignment of power of 2. so we use `std::bit_ceil()` to calculate
the minimum alignment greater or equal to the given number.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>