Build the libgoccia dynamic library and generated C header

Summary

Add a Pascal dynamic-library target named libgoccia that exports the C ABI from #864, together with a generated goccia.h.

Why

The build currently produces executables only. Foreign hosts need a loadable, versioned library artifact and a header that stays synchronized with its exported symbols.

Current behavior

There is no Pascal library target, exported symbol set, generated C header, ABI version metadata, or release artifact for embedding.

Expected behavior

• Add a Pascal library entry point exporting the #864 functions with the agreed calling convention.
• Produce libgoccia.dylib, libgoccia.so, and libgoccia.dll on supported platforms.
• Generate goccia.h from the canonical ABI definition and verify that header declarations match exports.
• Define ABI-major artifact/version conventions, symbol visibility, and runtime lookup/install-name behavior.
• Include the dynamic library and header in release packaging with checksums.
• Validate clean load/unload and repeated engine lifecycle before cross-language tests.

Scope notes

• Depends on #864 and is validated by #866.
• Cross-compilation enabling work is tracked by #238.
• Parent #823.
• Do not emit or document a static-library deliverable.

Start with the canonical ABI definition from #864 and inspect the repository's build and release configuration. Define the Pascal library target, generated goccia.h, artifact/version and symbol conventions, then validate loading and lifecycle behavior before the cross-language checks in #866; done includes platform libraries, header synchronization, release packaging, and checksums.