Since bytes is a very generic value that is returned from many calls,
it is easy to pass it by mistake to a function expecting a data_value,
and to get a wrong result. It is impossible for the data_value constructor
to know if the argument is a genuine bytes variable, a data_value of another
type, but serialized, or some other serialized data type.
To prevent misuse, make the data_value(bytes) constructor
(and complementary data_value(optional<bytes>) explicit.
Since row_cache::populate() uses allocating_section now, the trick
with populating under relcaim lock no longer works, resulting in
assertion failure inside allocating_section:
row_cache_alloc_stress: utils/logalloc.hh:289: auto logalloc::allocating_section::operator()(logalloc::region&, Func&&) [with Func = row_cache::populate(const mutation&)::<lambda()>::<lambda()>]: Assertion `r.reclaiming_enabled()' failed.
Use the trick with populating until eviction is detected by comapring
region occupancy.
