refactor: rename balius-proto -> balius-core, nest schema under proto::v0
The crate's job has been "the Balius-owned wire schema", but the name "balius-proto" advertised protobuf as the only thing it carries. `balius-core` is a roomier name for what is really the foundational types crate for the runtime <-> WASM interface — protobuf today, more things possibly later. The schema module also gets nested: `balius_proto::cardano` becomes `balius_core::proto::v0::cardano`. The `v0` segment makes the versioning explicit: this schema is wire-compatible with utxorpc-spec 0.17 by construction (the entire point of this PR), so it is frozen for pre-BigInt worker compat. A future breaking change to the schema goes under `proto::v1`, leaving `v0` consumers untouched. Mechanical changes: - Crate dir balius-proto/ -> balius-core/ - Package name -> balius-core; description updated - src/cardano.rs -> src/proto/v0/cardano.rs (plus new mod.rs files) - Workspace member + all 3 dependent Cargo.tomls updated (balius-runtime, balius-sdk, examples/asteria-tracker) - Import paths: balius_proto::cardano -> balius_core::proto::v0::cardano across balius-sdk, balius-runtime, examples/asteria-tracker - Doc/comment references updated No behavior change. cargo check --workspace --tests clean; 2/2 wire-compat tests in balius-core; 9/9 lib tests in balius-runtime (incl. all 8 u5c convert tests); e2e::faucet_claim still passes; only the pre-existing u5c-chainsync::wallet_balance stale-wasm failure remains. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>