computeTaskListState

Returns the worst NodeState that should be displayed for a TaskList containing the given tasks under the given priority.

"Expired and open" is what drives escalation; an open task counts as expired when either:

• it has a dueDate in the past (dueDate != null && dueDate <= now), or

• the server scheduler already fired it (expiredExecuted == true) — the recurring case, where dueDate may be null because the next fire time was computed from the cron expression and never persisted.

Tier rules:

• no expired-and-open tasks: NONE

• priority is HIGH and any expired-and-open task: SEVERE

• fixed-date overdue > 7 days: SEVERE

• fixed-date overdue 1–7 days: WARN

• otherwise (including recurring-only expiries without a dueDate): INFO

Returns early at SEVERE since no other tier can supersede it.