gcc complains about comparing a signed loop induction variable
with an unsigned limit, or comparing an expected value and measured
value. Fix by using unsigned throughout, except in one case where
the signed value was needed for the data_value constructor.
The test measures the time it takes to allocate a bunch
of small objects on LSA inside single segment.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>