This PR removes the cocoa, core_foundation and objc crates as dependencies, and replaces them with the objc2 family of crates.

On top of removing outdated dependencies and bringing us closer to the rest of the ecosystem, objc2 brings a couple benefits:

• Proper types throughout the codebase. objc exposed a lot of things as just id, and didn't manage null nor proper object retention at all.
• Way fewer instances of unsafe. objc2 provides simple safe wrappers for a lot of the simple operations.

The goal of this PR is to update the invocations while changing as little logic as possible. Further refactorings and code cleanups are needed, but will come in later releases.

I have tested those changes successfully on macOS 26.2. More testing is always welcome however. 🙂