Merge patch series "ns: header cleanups and initial namespace reference count improve...

Christian Brauner <brauner@kernel.org> says:

Cleanup the namespace headers by splitting them into types and helpers.
Better separate common namepace types and functions from namespace tree
types and functions.

Fix the reference counts of initial namespaces so we don't do any
pointless cacheline ping-pong for them when we know they can never go
away. Add a bunch of asserts for both the passive and active reference
counts to catch any changes that would break it.

* patches from https://patch.msgid.link/20251110-work-namespace-nstree-fixes-v1-0-e8a9264e0fb9@kernel.org:
  selftests/namespaces: fix nsid tests
  ns: drop custom reference count initialization for initial namespaces
  pid: rely on common reference count behavior
  ns: add asserts for initial namespace active reference counts
  ns: add asserts for initial namespace reference counts
  ns: make all reference counts on initial namespace a nop
  ipc: enable is_ns_init_id() assertions
  fs: use boolean to indicate anonymous mount namespace
  ns: rename is_initial_namespace()
  ns: make is_initial_namespace() argument const
  nstree: use guards for ns_tree_lock
  nstree: simplify owner list iteration
  nstree: switch to new structures
  nstree: add helper to operate on struct ns_tree_{node,root}
  nstree: move nstree types into separate header
  nstree: decouple from ns_common header
  ns: move namespace types into separate header

Link: https://patch.msgid.link/20251110-work-namespace-nstree-fixes-v1-0-e8a9264e0fb9@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>