The maximum number of bytes we are willing to buffer when reading an API
response from an iroh QUIC stream. This must be large enough to accommodate
the largest possible signed session outcome. A session can contain up to
broadcast_rounds_per_session (default 3600) rounds, each peer produces one
unit per round, and each unit can be up to ALEPH_BFT_UNIT_BYTE_LIMIT
bytes. The response is JSON-serialized which hex-encodes the consensus
bytes, roughly doubling the size. We use 2x the raw max as a conservative
upper bound. For a 4-peer federation this is ~1.44 GB.