now that we are allowed to use C++23. we now have the luxury of using
`std::ranges::stable_partition`.
in this change, we:
- replace `boost::range::stable_parition()` to
`std::ranges::stable_parition()`
- since `std::ranges::stable_parition()` returns a subrange instead of
an iterator, change the names of variables which were previously used
for holding the return value of `boost::range::stable_partition()`
accordingly for better readability.
- remove unused `#include` of boost headers
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21911
93be8f3a0c