Previous code performed endian conversion by bulk-copying raw bytes
into a std::vector<float> and then iterating over it via a
reinterpret_cast<uint32_t*> pointer. Accessing float storage through a
uint32_t* violates C++ strict aliasing rules, giving the compiler
freedom to reorder or elide the stores, causing undefined behavior.
Replace the two-pass approach with a single-pass loop using
seastar::consume_be<uint32_t>() and std::bit_cast<float>(), which is
both well-defined and auto-vectorizable.
Follow-up #28754Closesscylladb/scylladb#28912