Invalid schedules/configs create checkpoints

[VeckoTheGecko]

Describe the bug
The checkpoint mechanism isn't really clear to me - currently running with an invalid schedule creates the checkpoint YAML

To Reproduce
Steps to reproduce the behavior:

• virtualship init test
• cd test
• virtualship run .

❯ virtualship run .     
[TIMER] Expedition started...

╔═════════════════════════════════════════════════╗
║          VIRTUALSHIP EXPEDITION STATUS          ║
╚═════════════════════════════════════════════════╝

---- WAYPOINT VERIFICATION ----

Verifying route... 
... All good to go!

Waypoint 5 could not be reached in time. Current time: 1998-01-01 03:00:14.987829. Waypoint time: 1998-01-01 03:00:00.

Have you ensured that your schedule includes sufficient time for taking measurements, e.g. CTD casts (in addition to the time it takes to sail between waypoints)?

Hint: previous schedule verification checks (e.g. in the `virtualship plan` tool or after dealing with unexpected problems during the expedition) will not account for measurement times, only the time it takes to sail between waypoints.

Please update your schedule (`virtualship plan` or directly in expedition.yaml) and continue the expedition by executing the `virtualship run` command again.
Checkpoint has been saved to checkpoint.yaml.

• Update the schedule.yaml updating the timing so there's 1D between each
• virtualship run .

(VirtualShip) (base) 🦎ship/test   problems-nick[$?] ❯ virtualship run .
[TIMER] Expedition started...

╔═════════════════════════════════════════════════╗
║          VIRTUALSHIP EXPEDITION STATUS          ║
╚═════════════════════════════════════════════════╝
Traceback (most recent call last):
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/bin/virtualship", line 10, in <module>
    sys.exit(cli())
             ^^^^^
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/lib/python3.12/site-packages/click/core.py", line 1485, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/lib/python3.12/site-packages/click/core.py", line 1406, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/lib/python3.12/site-packages/click/core.py", line 1873, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/lib/python3.12/site-packages/click/core.py", line 1269, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Hodgs004/coding/repos/ship/.pixi/envs/default/lib/python3.12/site-packages/click/core.py", line 824, in invoke
    return callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Hodgs004/coding/repos/ship/src/virtualship/cli/commands.py", line 108, in run
    _run(Path(path), prob_level, from_data)
  File "/Users/Hodgs004/coding/repos/ship/src/virtualship/cli/_run.py", line 95, in _run
    checkpoint.verify(expedition, problems_dir.joinpath(LOG_DIR))
  File "/Users/Hodgs004/coding/repos/ship/src/virtualship/models/checkpoint.py", line 78, in verify
    raise CheckpointError(
virtualship.errors.CheckpointError: Past waypoints in schedule have been changed! Restore past schedule and only change future waypoints (waypoint 5 onwards).

Expected behavior
I expected no checkpoint file to be created on an invalid schedule

Additional context
Add any other context about the problem here.