fix(sidecar): preserve Redacted values across RPC serialization

[schutzelaars]

Ran into this while testing the Vite + Cloudflare Worker setup from #331 (feat(cloudflare): vite dev). On alchemy dev, Redacted values sent through the sidecar RPC arrive on the worker side as the literal string "<redacted>".

Anything passing a Redacted through a binding hits this. In my case, Hyperdrive's password:

Cloudflare.Hyperdrive("db", {
  origin: { ..., password: secret /* Redacted<string> */ },
});

→ password authentication failed.

JSON.stringify calls toJSON() before the replacer, and Redacted.toJSON() returns "<redacted>", so this replacer in Sidecar/RpcHandler.ts never fires:

JSON.stringify(args, (_, value) => {
  if (Redacted.isRedacted(value)) {
    return { _tag: "Redacted", value: Redacted.value(value) };
  }
  return value;
});

Deserialize side already handles the { _tag: "Redacted", value } envelope.

Fix

Pre-walk the args with encodeRedacted before JSON.stringify:

• recurses into arrays, plain objects, and the inner value of nested Redacted
• skips objects with their own toJSON (Date, URL, …) so JSON.stringify keeps using their custom shape

Covered by packages/alchemy/test/Sidecar/RpcHandler.test.ts: top-level Redacted, Redacted nested in an object, and a Date arg (exercises the toJSON skip).