feat: add onRiveReady callback to useRive hook

[damzobridge]

This PR adds an onRiveReady callback to the useRive hook. There's already an onLoad callback in the hook's UseRiveParameters, however, it doesn't include the rive object, so users can't set inputs or do anything within that callback.

So this adds a version of the callback that includes the Rive object.

const { rive, RiveComponent } = useRive({
    src: 'rating.riv',
    stateMachines: 'State Machine 1',
    autoplay: true,
    automaticallyHandleEvents: true,
    onRiveReady: (rive) => {
      console.log('Rive loaded', rive);
      const inputs = rive.stateMachineInputs('State Machine 1');
      inputs.forEach(i => {

        if (i.name === "rating") {
          i.value = 3;
          return;
        }
      });
    }
  });

This lets users set initial values on the rive file before the first render, which is important for some rive graphics that expect values to show up immediately.

[damzobridge]

Something to think about:

• This PR adds the callback to UseRiveOptions rather than UseRiveParameters.
  Using it with the hook would look like this if moved to UseRiveParameters:

const { rive, RiveComponent } = useRive({
    src: 'rating.riv',
    stateMachines: 'State Machine 1',
    autoplay: true,
    automaticallyHandleEvents: true,
    onLoad: (rive) => {
      const inputs = rive.stateMachineInputs('State Machine 1');
      inputs.forEach(i => {

        if (i.name === "rating") {
          i.value = 3;
          return;
        }
      });
  }
  });

Curious what you think @HayesGordon ?

[HayesGordon]

I think your current option feels more Reacty? But the second would increase discoverability. I'm fine with both.

[HayesGordon]

LGTM!

[HayesGordon]

Looks even better!