Macro derive

Apply derive macros re-exported by rustmax.

Most derive macros generate code that names their own crate, which fails when the crate is reached through rustmax instead of being a direct dependency. This attribute rewrites the derive paths and injects whatever each derive crate needs to find its runtime.

#[rmx::derive(Serialize, Deserialize, Clone, Debug)]
#[serde(rename_all = "camelCase")]
struct Config {
    some_field: u32,
}

Names it does not recognize are passed through to #[derive(..)] unchanged, so built-in and third-party derives can be listed alongside.