This diff renaming the Rust code directory from `rust-notifications` to `rust-lib` name, because we are going to use a single Rust library with the submodules instead of building separate Rust libraries.
This is a part of the stack.
The full context is available in the Linear task.
Related Linear task: [[ https://linear.app/comm/issue/ENG-1895/change-to-use-a-single-rust-code-library-to-c-code-instead-of-a-few | ENG-1895 ]]