Signing C2PA images via DigiCert CSC API using Rust FFI

Use Rust-based FFI library to remotely sign C2PA Manifests using Document Trust Manager CSC APIs and embed signed manifests to images. The library exposes FFI-safe functions that can be called from Java or other languages via JNI or other FFI mechanisms. Rust FFI (Foreign Functions Interface) works with any language that calls C libraries (C, C++, Python, Java, C#, Go, Swift, Ruby, etc).