Problem

Alchemy rate limit errors (HTTP 429) only log the status code, not the detailed error message from the response body.

This is hard to debug.

Current log:

HTTP error: 429 Too Many Requests

Alchemy response body contains:

{"error": {"code": 429, "message": "Monthly capacity limit exceeded. Visit https://dashboard.alchemy.com/settings/billing..."}}

Location: https://github.com/ithacaxyz/relay/blob/main/src/chains.rs#L435

Parse and log the error.message field from JSON-RPC error responses.