Fix failure mechanics in checkpoint example

[andrewwdye]

Signed-off-by: Andrew Dye [email protected]

TL;DR

The checkpoint example is not behaving correctly when n_iterations is not an exact multiple of RETRIES due to use of float. Fix the logic to choose a failure interval of n_iterations // RETRIES.

Testing

Verified running locally raises an exception on iteration (as expected) and that workflow succeeds when running with pyflyte run --remote checkpoint.py example --n_iterations 10.