managed_bytes: fix potentially unaligned accesses
managed_bytes: fix potentially unaligned accesses

blob_storage defined with attribute packed which makes its alignment
requirement equal 1. This means that its members may be unaligned.
GCC is obviously aware of that and will generate appropriate code
(and not generate ubsan checks). However, there are few places where
members of blob_storage are accessed via pointers, these have to be
wrapped by unaligned_cast<> to let the compiler know that the location
pointed to may be not aligned properly.

Signed-off-by: Paweł Dziepak <e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>

kjniemi/scylla,kjniemi/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,kjniemi/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,raphaelsc/scylla,duarten/scylla