Fix DNS leaks, lifecycle race, and editor arg splitting

- DNS Leak / Isolation Bypass: Blocked glibc's systemd-resolved and
  D-Bus socket communication within the unprivileged mount namespace by
  introducing BlockHostServices(). This targeted mount-blocking forces
  glibc to fall back to the standard resolv.conf DNS routing path and
  prevents host leaks.
- Lifecycle Race: Reordered and protected the reference-counting
  cleanup routine under the profile flock to ensure that check-and-unpin
  operations are atomic and do not teardown namespaces actively used
  by parallel processes.
- Editor Arguments: Split the EDITOR environment variable into discrete
  field tokens before invocation to support editor configurations
  containing command-line flags.
- Testing: Added E2E regression tests for DNS leak detection,
  namespace unpinning concurrency, and editor argument parsing. All E2E
  tests now compile and pass cleanly.

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