tools/memcached_benchmark: bump lockfile and upgrade slab to version …

…0.4.11

The get_disjoint_mut method in slab v0.4.10 incorrectly checked if
indices were within the slab's capacity instead of its length, allowing
access to uninitialized memory. This could lead to undefined behavior or
potential crashes.

Upgrade slab to version 0.4.11

Signed-off-by: Ruowen Qin <chinqrw@gmail.com>

Rex Kernel Extension v2025.08.13