Add Runtime Shell Binary for Fast ink! E2E Tests

[Daanvdplas]

Summary

runtime-only tests currently compile the runtime that is used every time developers run cargo test, which makes the fast-path unusable on large projects. We need a precompiled “runtime shell” binary that embeds the ink parachain runtime, exposes the same contract RPC endpoints as ink-node, and lets ink-e2e execute contracts natively without spawning a node or recompiling the runtime.

Desired Solution

Build a new binary crate (e.g. ink-runtime-shell) that:

• Depends on ink_parachain_runtime and TestExternalities.
• Initializes genesis state in memory and runs the runtime natively via ext.execute_with.
• Exposes the Contracts_* JSON-RPC methods (upload_code, instantiate, call, tracing/dry run) identical to ink-node’s RPC surface.
• Listens on a localhost port; ink-e2e spawns it exactly like the node process today.

Ink-e2e’s runtime-only backend should be able to toggle between this shell and ink-node, reusing the existing RPC client. The shell should be shipped as a precompiled artifact (similar to ink-node releases) so developers download it once; their contract tests then link only their own code and run at native speed.

Benefits

• No runtime compilation during cargo test → faster dev iterations.
• Same behavior/API as the node path → no special client logic.
• No spawning of node compared to using ink-node

Acceptance Criteria

• ink-runtime-shell binary runs locally and answers contract RPCs using the native runtime.
• the e2e and sandbox crate should be refactored into one crate and the only thing that should differ is interacting with the ink-node or ink-runtime-shell