Fix support request: ConnectionResetError

Beacon crashes when receiving more than 10 simultaneous requests, and returns a 500 error when queries include filters (e.g. SNOMED codes or Gender).

Two bugs were identified:

. The SQLAlchemy async engine was created with default pool settings (pool_size=5, max_overflow=10), which is insufficient for concurrent usage. Under load, all connections get exhausted and new requests fail.

. The peek() utility function in utils.py only accepted iterators/generators. When checkFilters() passes a plain list, next() raises a TypeError, causing a 500 Internal Server Error on any filtered query.