velocity-hive-common v0.1.0

First taggable release of the extracted Hive primitives crate.
Pinning rev for the bridge sibling's bridge-hive consumption per
their request in
siblings-comms/blockchain/velocity-hive-common-shipped-acked.md.

Includes:
- tx: HiveTransaction + binary serializer + varint/string helpers
- sign: PostingKey + WIF + canonical-signature retry loop
- client: sync HiveClient (default)
- client_async: HiveAsyncClient behind the `async` feature flag

41 unit tests passing across both feature configurations.