Task/Issue URL: https://app.asana.com/1/137249556945/project/72649045549333/task/1215729137633076?focus=true

Description

Replaces two Thread.sleep(...) calls in the sync v2 retry-backoff loops with delay(...):

• ThirdPartyCredentialManager.retryingOnRateLimit (used when extending the account with a 3party credential and the server rate-limits the call)
• SyncAccountRepository.retryingOnTransientError (used during the 3party → ddg upgrade login)

Switching to delay required a suspend cascades a little to these:

• ThirdPartyCredentialManager.create()
• SyncAccountRepository.createThirdPartyCredential() and joinAccountFromThirdPartyRecoveryCode()
• RecoveryCodeProvider.createThirdPartyCredentialIfNeeded()
• A small refactor inside ExchangeV2Runner.shareRecoveryCodeAndAdvanceLocked so the recovery-code fetch+send runs inside the launched coroutine instead of synchronously before it.

Intentional behaviour changes

• SM mutex no longer held during the recovery-code fetch+send. In shareRecoveryCodeAndAdvanceLocked, the network work now runs inside the launched coroutine and outside mutex.withLock, so retry backoff doesn't block the dispatcher thread. A short-circuit at the top of the launch handles the common cancel-before-run race; any work that proceeds past it is best-effort, and any orphaned server-side credential is cleaned up by the BE's 5-min TTL.

Steps to test this PR

• Manual: sync with a 3rd party browser

UI changes

None.