3.4.0

• Gafaelfawr now uses async SQLAlchemy for all database calls, which avoids latency affecting the whole process when a request requires database queries or writes.
• Internal and notebook tokens are now acquired, when needed, while holding a per-user cache lock. This means that when a flood of requests that all require a delegated token come in at the same time, a given Gafaelfawr process allows only the first request to proceed and blocks the rest until it completes. All the other requests are then served from the cache. This fixes a deadlock observed in previous versions of Gafaelfawr under heavy load from a single user who does not have a cached delegated token.
• Update dependencies.