Runtime-agnostic SDK (V8/Edge support)

I want the creem_io SDK to be compatible with V8/Edge runtimes (like Convex, Cloudflare Workers) by removing Node-exclusive dependencies. Currently, it relies on Node globals/libraries, which forces users to run in Node environments, increasing latency and cold starts. Since the SDK is primarily a typesafe fetch wrapper, making it runtime-agnostic would be a significant improvement.