CON-382: Feedback on FFI conventions

[alejnp]

There are some idioms in Rust more suitable for our code, such as using std::ptr::NonNull.
We should prefer these to enforce a safer and cleaner code.

• Native{} now holds a NonNull<T> instead of a *const T.
• FFI calls that take a pointer "self" argument prefer NonNull<T>, because the C API expects non-null and NonNull<T> is transparent over *const T.

Additionally, we could use the chance to revisit the naming conventions on FFI-related types to better reflect their nature.

• Native{} --> Ffi{}: "Native" could refer to anything, but FFI implies "glue".
• {}Ptr --> Opaque{}: The types were never pointers to begin with.

[Copilot]

Pull request overview

This PR refactors FFI-related types and conventions to improve code safety and clarity in the Rust DDS Connector codebase. The changes adopt more idiomatic Rust patterns for FFI, specifically using std::ptr::NonNull<T> for non-null pointer guarantees and improving naming conventions to better reflect the nature of FFI types.

Changes:

• Renamed wrapper types from Native{} prefix to Ffi{} prefix (e.g., NativeConnector → FfiConnector) to better indicate FFI glue code
• Renamed opaque C types from {}Ptr suffix to Opaque{} prefix (e.g., ConnectorPtr → OpaqueConnector) to clarify they are opaque types, not pointers
• Changed FFI function parameters from raw pointers to NonNull<T> for non-null pointer parameters, providing compile-time safety guarantees

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/ffi/rtiddsconnector.rs	Updated opaque type names and FFI function signatures to use NonNull<T> for non-null parameters; changed return type constness for consistency
src/ffi/mod.rs	Renamed wrapper types from Native{} to Ffi{}, updated internal storage to use NonNull<T>, and adjusted usage patterns with NonNull::new()
src/connector.rs	Updated references from NativeConnector to FfiConnector throughout

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