data store: task state totals should only represent n=0

[oliver-sanders]

This is related to the redesign/rethink of the workflows sidebar in cylc-ui. See cylc/cylc-ui#2331, cylc/cylc-ui#2350

Workflow task state counts are currently computed for the whole n-window. We think it would make more sense for the workflow state totals to only represent n=0 tasks. This way:

• Changing the n-window doesn't change the state count.
• Failed/submit-failed, but completed tasks are not included in the failed/submit-failed counts.
• Makes it easier to support is_held and is_retry counts (note, historical tasks may be held, but displaying this might not be considered helpful).

As this is data-store only, we feel this is something we can put into a bugfix release.

[dwsutherland]

PR up:
#7075

[hjoliver]

Agreed with the premise.

[wxtim]

Failed/submit-failed, but completed tasks are not included in the failed/submit-failed counts.

This probably needs to be a .. warning:: somewhere in the documentation (workflow style guide? section on optional outputs and handling failure).

[oliver-sanders]

Closed by #7075