Make `onComplete` more type safe

[sujayakar]

It currently only has any for the function return type. Instead, we could have developers define the callback with an onComplete wrapper instead of internalMutation:

export const exampleCallback = onComplete({
  action: internal.index.exampleAction, 
  handler: async (ctx, args) => {
});

Then, args would have its type specified precisely.

To support custom functions, onComplete could take in internalMutation:

const onComplete = makeOnComplete(internalMutation);

[sujayakar]

Another idea from https://github.com/get-convex/action-retrier-component/pull/1/files/2e20e8f50b95f5f724a69a1d77ad79c498c76ddb#r1766109004 --

Add a type parameter (or regular parameter) to runResultValidator to parameterize it on the action that's being retried. Then, it can know the action's return type more precisely.