…rk-failure retry

Brings registerToken to feature parity with disablePush (shipped under
SDK-297): the registration request is now persisted to the offline task
queue and replayed when the network returns, instead of being dropped
fire-once on transient network failures.

Implementation mirrors the SDK-297 disableDevice retrofit:
- Adds `register(...)` to `RequestProcessorProtocol` (taking the
  already-resolved `notificationsEnabled: Bool`, not the async
  notification-state provider) so both processors can implement it and
  `sendUsingRequestProcessor` can pick offline vs online at call time.
- Adds `RequestIdentifier.registerToken` (sibling to the existing
  `disableDevice` identifier).
- Implements `register(...)` in `OfflineRequestProcessor` using the
  existing `RequestCreator.createRegisterTokenRequest(...)` +
  `sendIterableRequest(...)` pattern.
- Updates `OnlineRequestProcessor.register(...)` to conform to the new
  protocol signature and consume the shared identifier; the existing
  private register helper is folded into the public one.

The notification-state wrinkle (parallel to SDK-297's
`UserIdentitySnapshot`): `notificationStateProvider.isNotificationsEnabled`
is now resolved inside `RequestHandler.register` BEFORE routing to a
processor. The resolved bool is captured into the offline task body at
schedule time, so a request queued offline and replayed later carries
the bool as it was at call time — replay does NOT re-query notification
state.

Public IterableAPI / InternalIterableAPI surface and Obj-C selectors are
unchanged. Tests in `offline-events-tests` cover (a) offline replay with
the expected body, and (b) the snapshot semantic — a
`MockNotificationStateProvider` flipped from `true` to `false` after
register is called still yields `notificationsEnabled: true` on the
replayed request.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Address review: register now captures a UserIdentitySnapshot synchronously
before the async notification-state callback and deferred processor
selection, mirroring disableDeviceForCurrentUser. This ensures the
register request targets the user who was current at call time rather than
whoever live auth points to when the deferred/offline build resolves.

The snapshot threads through both the online and offline paths into
RequestCreator.createRegisterTokenRequest, which applies it (and derives
preferUserId from the .userId case) instead of reading live auth. Callers
that pass no snapshot keep the previous live-auth behavior and the
auth-missing guard.

Tests: register at call time then mutate/clear identity before the deferred
callback resolves; assert both offline-replay and online-fallback requests
still carry the call-time identity and preferUserId.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Drop the cross-layer UserIdentitySnapshot threading. Capture call-time auth
once in RequestHandler.register and carry it on RegisterTokenInfo.auth;
RequestCreator resolves registerTokenInfo.auth ?? self.auth through the
existing single body path. Reverts the snapshot parameter on ApiClient, the
processors, and the protocol.

Register offline tasks are purged on logout (only disableDevice is
preserved), so the full disableDevice snapshot symmetry was unnecessary.
Keep an upfront identity guard in register: dropping it would regress
onFailure on the offline no-user path, since the callback only attaches
after a task is scheduled.

Build green; offline RequestHandlerTests 36/0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…r-token-offline-retry

* origin/master:
  SDK-300 Add OnSuccess/OnFailure handlers to logoutUser (#1069)
  SDK-469 Fix CodeQL string length conflation in deep link check (#1071)
  SDK-493: Prepare for Release 6.7.2 (#1070)