Fix get_output_mana_rewards, clippy

[Thoralf-M]

Description of change

Fix get_output_mana_rewards, the slot query param was wrong (slotIndex instead of slot, clippy

Type of change

• Bug fix (a non-breaking change which fixes an issue)

How the change has been tested

        const commitment = await client.getOutputManaRewards(
            '0x980709653c07932d28dfeda348243e92de5d1bb7ca9cffbfac069c214ef271a9000000000300',
            300000,
        );
        console.log(commitment);