Merge patch series "ns: minor tweaks"

Christian Brauner <brauner@kernel.org> says:

* Add a missing include into the cgroup namespace header.
* Simplify ns_common_init{_inum}() and derive the namespace operations
  from the namespace type.
* Add debug asserts into ns_common_init{_inum}() to catch bugs.

* patches from https://lore.kernel.org/20250922-work-namespace-ns_common-fixes-v1-0-3c26aeb30831@kernel.org:
  ns: add ns_debug()
  ns: simplify ns_common_init() further
  cgroup: add missing ns_common include

Signed-off-by: Christian Brauner <brauner@kernel.org>