op-sync-tester: Strict Mode

Add a mode for checking the authentication from the CL. Sync tester validates the JWT against a shared HMAC secret. Requests with a missing or invalid token return an authentication error. In this case, sync tester must hold the valid JWT.

Only applied against the engine namespace.

Start at the op-sync-tester CLI entry point and trace its request authentication and JWT validation flow. Confirm how the engine namespace is selected, then define done as retaining a valid JWT for that namespace while missing or invalid tokens produce an authentication error.

Written by the indexing model from the issue text.