Add method to RetryException to get a typed last Attempt

[sleberknight]

Currently to get the result of the last failed attempt in a RetryException you need a cast:

var result = (Integer) retryException.getLastFailedAttempt();

To avoid this and make the API a bit nicer, add a method to RetryException to get the last failed Attempt with a specific type:

// result has inferred type of Integer
var result = retryException.getLastFailedAttempt(Integer.class);

// or define the type explicitly
Integer result = retryException.getLastFailedAttempt(Integer.class);

Of course, the caller must know the actual type or else a ClassCastException is thrown, but that's just Java...

[sleberknight]

This was added as the "fix" to Should Attempt even have a type parameter?