Transfer-context lookup by original_call_sid ran
`redis.keys("transfer:context:*")` and iterated every match — an O(N)
blocking scan on call-control hot paths, duplicated across the ARI
manager and the Twilio/Telnyx conference strategies.
Maintain a `transfer:by_call_sid:{original_call_sid}` -> transfer_id
secondary index, written and cleared alongside the context in
store/remove, and resolve lookups with a direct GET. Route the
Twilio/Telnyx strategies through the manager so the lookup lives in one
place (also dropping per-call ad-hoc Redis connections).
Closes#328
Co-authored-by: shiminshen <16914659+shiminshen@users.noreply.github.com>
