/// Returns the Uniform Resource Identifier (URI) for `token_id` token.
    ///
    /// NOTE: In order to expose this function in the ABI, you need to annotate
    /// it with `#[selector(name = "tokenURI")]` and ensure that the `erc721`
    /// parameter is passed internally. This design works around Stylus's lack
    /// of inheritance while avoiding code duplication. See the Example section.
    ///
    /// # Arguments
    ///
    /// * `&self` - Read access to the contract's state.
    /// * `token_id` - ID of a token.
    /// * `erc721` - Read access to a contract providing [`IErc721`] interface.
    ///
    /// # Errors
    ///
    /// * [`Error::NonexistentToken`] - If the token does not exist.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// #[selector(name = "tokenURI")]
    /// pub fn token_uri(&self, token_id: U256) -> Result<String, Vec<u8>> {
    ///     Ok(self.metadata.token_uri(token_id, &self.erc721)?)
    /// }
    /// ```