feat(protocol): encode transaction logs in canonical protobuf

[partylikeits1983]

Adds protobuf transport for the transaction logs introduced by the preceding PRs. Proven transactions now encode their submitted TransactionLogData, and transaction headers carry the corresponding commitment. Public submissions contain complete transaction logs; private submissions contain only a commitment.

Local execution data has a separate purpose: transaction arguments retain the secret salt, and transaction effects retain the complete transaction logs and salt needed for local processing. Those messages can contain private data and are not the public transaction submission format.

Please focus review on:

• Canonical decoding and bounds. Transaction log byte fields use the canonical Rust serialization adapters, which reject malformed encodings and trailing data while preserving the transaction log size checks.
• Privacy at the transport boundary. Private proven transactions must carry neither transaction log payloads nor the secret salt. Local arguments and effects intentionally retain those values.
• Field propagation. Encoding, decoding, and domain object construction must preserve the transaction header commitment and apply the existing visibility and commitment checks. The generated type adapters are imported in the modules where the protobuf code is included.

Part 4 of 4. Depends on #3903. Stack: #3833 → #3902 → #3903 → #3904.

Batch and block transaction log transport, including aggregate size limits, is deferred to the separate draft PR #3905. This stack provides transaction execution, proof and signature binding, and transaction protobuf support; it does not provide block storage or query APIs for transaction logs.

Closes #3831.