DSA size returns maximum size of signature

    private_key_to_der!(ffi::i2d_DSAPrivateKey);

    public_key_to_der!(ffi::i2d_DSAPublicKey);

    /// Returns the size of the signature output by `self` in bytes.  Returns

    /// Returns the maximum size of the signature output by `self` in bytes.  Returns

    /// None if the keys are uninitialized.

    ///

    /// OpenSSL documentation at [`DSA_size`]