test: add Arc fixture exporter for Leafage

[littlehand26]

Summary

• add an ignored launched-node exporter for reusable Arc-to-Leafage fixtures
• validate genesis, empty hooks, native transfer, CREATE/CREATE2, and failed CREATE semantics before writing captures
• generate RPC, gzip JSON, RLP StateDiff, and bundle-0 artifacts with fail-closed provenance checks
• add an opt-in synchronous state-root path for this in-process exporter while preserving the default setup behavior

Motivation

Leafage Arc ingestion and RPC tests need producer-captured bytes rather than hand-authored fixtures. This stacked test-only PR makes those artifacts reproducible from the protocol-correct writer in #4 and records the exact producer, transformer, and format reference inputs.

Testing

• two independent launched-node exporter runs: 1/1 each, no deferred-trie/background panic
• normalized block 0..4 payload hashes stable across both runs
• cargo fmt --all -- --check
• cargo test --locked -p arc-execution-e2e --test export_leafage_a1b --no-run
• bash -n scripts/generate-leafage-a1b-fixtures.sh
• Python compile, panic-detection self-test, and provenance positive/negative tests
• git diff --check

Compatibility

The new state-root option defaults to false. Existing execution E2E tests and production behavior are unchanged. StorageCleared, Zero7/8, and CallFrom are intentionally outside this fixture set.

[littlehand26]

Superseded by #7. The replacement branch descends from #6, updates the producer baseline to the canonical genesis-ID fix, and passed the two-capture provenance/determinism gate. This PR branch and commits are retained for history; no force-push or deletion was performed.