Embeddable libgoccia dynamic library (C, Rust, Crystal, Nim, C#)

Summary

Expose GocciaScript through a versioned libgoccia dynamic library with a stable C ABI so non-Pascal hosts can embed the engine.

Why

The project is embeddable from FreePascal today, but there is no exported library boundary for C, Rust, Crystal, Nim, C#, or other FFI-capable hosts.

Expected behavior

• Ship libgoccia.dylib, libgoccia.so, and libgoccia.dll for supported platforms.
• Publish a generated goccia.h describing the stable exported ABI.
• Version the ABI and dynamic-library artifact independently from internal Pascal units.
• Prove lifecycle, evaluation, function calls, value marshalling, error handling, and handle ownership from real foreign callers.

Scope notes

• Design: #864.
• Dynamic-library target and header: #865.
• Cross-language validation: #866.
• Documentation and examples: #867.
• Cross-compilation sustainability: #238.
• This track does not produce or promise a static library.

Start with the design in #864 and the dynamic-library and header scope in #865, then review the cross-language validation in #866 and documentation examples in #867. Done means supported platforms ship versioned libgoccia artifacts and goccia.h, with foreign-caller coverage for lifecycle, evaluation, calls, marshalling, errors, and ownership.