Simplify fastforward/start/end/time handling

Remove --fastforward

Now we just use --start and --end. For replay --start defaults to the beginning of the dataset. For generated workloads it defaults to 2000-01-01.

Most the tests are passing, but there are now 3 test failures:

• test_main_network_run[lassen] This has been failing for a while
• test_main_withdata_range_run[gcloudv2] and test_main_withdata_run[gcloudv2]
  • This test is failing now that I added a few extra checks in the tests. I don't think the failure is caused by this PR, it has the same problem on current develop. It appears that the gcloudv2 loader isn't actually loading any jobs into the engine? The dataloader is returning a list of jobs but the engine seems to just be skipping them all. I'm not sure whats going on there.