Add WASM bindings (offline DIGStore spend bundles) + npm package CI

[MichaelTaylor3d]

Summary

Adds WebAssembly bindings to datalayer-driver that mirror the offline subset of the existing NAPI interface, published as the npm package @dignetwork/datalayer-driver-wasm via CI. Primary use case: build and sign DIGStore (DataStore) spend bundles client-side in the browser/bundler environments, producing byte-for-byte identical output to the NAPI bindings.

What changed

• Core crate (native feature gating): new default-on native cargo feature gates all networking (tokio, chia-wallet-sdk native-tls/peer-simulator, every &Peer async fn). The chia meta-crate (which transitively pulls chia-client→tokio) was decomposed into wasm-safe sub-crates so the core crate compiles to wasm32-unknown-unknown. Native + NAPI builds are unchanged.
• New wasm/ workspace member: wasm-bindgen crate exposing ~30 offline functions — key derivation, address codecs, coin selection, DIGStore spend builders (mintStore/oracleSpend/meltStore/updateStoreMetadata/updateStoreOwnership), signing, serialization, server coins. JS shape matches NAPI exactly: Uint8Array for bytes, bigint for amounts (BigInt-configured serializer — mojo amounts exceed 2^53), camelCase fields.
• Parity test (wasm/tests/parity.mjs): loads both the NAPI .node and the WASM nodejs build and asserts byte-for-byte equality across the offline surface, including a full mintStore → signCoinSpends → spendBundleToHex bundle, plus meltStore/sendXch/signMessage/verifySignedMessage.
• Packaging: wasm-pack --target bundler --release + a patch script that sets the scoped package name and ships a hand-written, complete typed .d.ts.
• CI: new build-wasm job (installs clang/lld for blst, builds, runs the parity test) and publish-wasm-npm job (version-tag-gated, mirrors the existing publish-npm pattern). Existing rust-checks (clippy -D warnings, cargo machete, fmt) remain green.

Scope notes

• Offline only — no Peer/Tls/networking (WASM has no native sockets). Chain I/O stays the JS consumer's responsibility.
• One intentional, documented deviation: DataStoreMetadata.sizeProof output is the symmetric 32-byte form (correct, round-trips) rather than replicating a NAPI output bug. Field type remains Uint8Array (matches NAPI).
• Known follow-up: build:bundler uses --no-opt because the bundled wasm-opt rejects blst's bulk-memory ops; re-enable with a wasm-opt that supports --enable-bulk-memory for size optimization.

Design spec: docs/superpowers/specs/2026-05-29-datalayer-driver-wasm-bindings-design.md
Implementation plan: docs/superpowers/plans/2026-05-29-datalayer-driver-wasm-bindings.md

Test Plan

• cargo build -p datalayer-driver --target wasm32-unknown-unknown --no-default-features succeeds
• cargo build -p datalayer-driver and -p datalayer-driver-napi succeed (no native regression)
• cargo clippy --all-targets --all-features -- -D warnings, cargo machete, cargo fmt --all -- --check pass
• WASM↔NAPI parity test passes byte-for-byte (mint bundle, melt, sendXch, sign/verify, keys, addresses, cost, coin id)
• wasm-pack build --target bundler --release + patch produces @dignetwork/datalayer-driver-wasm@3.0.0
• CI build-wasm job green on this PR
• (release) publish-wasm-npm publishes on a version-tag commit

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