/// Compile-time metadata about which fields or variants require capabilities.
///
/// This trait is generated by `#[derive(AuthSchema)]` from the
/// `mcp-authorization-macros` crate. Each `#[requires("capability")]`
/// annotation on a struct field or enum variant produces an entry in the
/// returned static slice.
///
/// You can also implement this manually:
///
/// ```
/// use mcp_authorization::AuthSchemaMetadata;
///
/// struct MyInput {
/// pub name: String,
/// pub secret_field: Option<String>,
/// }
///
/// impl AuthSchemaMetadata for MyInput {
/// fn requirements() -> &'static [(&'static str, &'static str)] {
/// &[("secret_field", "admin")]
/// }
/// }
/// ```