Splits ProtocolMessages exceeding NIP-44's 65,535-byte plaintext ceiling
across multiple gift-wrapped events. Symmetric (both directions),
fire-and-forget, backward-compatible via a new transport-level
\`extensions\` field on \`dapp_ready\` and \`wallet_ready\`. Resolves the
\"Failed to swap: invalid plaintext size\" error on aggregated swap
requests and enables signed-tx responses up to the 1 MB BCH consensus
limit (~2 MB hex).
This backward compatible change allows wallets/dapps to add additional
features outside the basic transaction signature support to the
hdwalletv1 protocol.
Canonical encoding for BigInt (<bigint: Xn>) and Uint8Array (hex or
<Uint8Array: 0x...>) used in the relay protocol. Provides both
serialization (sourceOutputToRelay, transactionToHex) and deserialization
(parseExtendedJson, toUint8Array, toBigInt) so dapps and wallets
don't have to implement this independently.
