Rerun C API

The Rerun C library provides a minimalistic C interface that encapsulates the shared building blocks of all Rerun SDKs. It's a key dependency of the Rerun C++ SDK, serving as the primary language interface into the Rust codebase.

⚠️ It currently serves exclusively this language binding purpose. It is not a full SDK yet as there's no utilities for serializing data for logging any of the built-in types. As of now it can only log raw Arrow IPC messages.