LBFGS - Add functionality to skip updates

Would it be possible to add the ability to skip updates to the lbfgs algorithm, in case a certain curvature condition does not hold? You can find the relevant information on page 537 of the book "Numerical Optimization" by Nocedal and Wright.

While it isn't great to skip updates, it prevents the algorithm from breaking when the Wolfe conditions are not satisfied (sometimes, one needs to use backtracking line search due to computational restrictions).

This would mean to add about 20 lines to the existing optax code - I'm happy to provide my current implementation.