qkc/types: support versioned cross-shard transaction lists

[ping-ke]

Problem

CrossShardTransactionList decoding was tied to a specific data structure. Adding a new version or new fields would break compatibility with older data.

Solution

This PR adds version-based serialization and decoding:

• Serialization uses the latest structure and writes the version in the last four bytes, matching pyquarkchain.
• Decoding reads the version first and uses the matching structure.
• Older versions are converted to the latest CrossShardTransactionList.
• Adding a new version only requires a new versioned structure and decoding case, without affecting older data.