OccurrenceIter retry loop is expensive for degenerate rules

[eikopf]

Location

crates/gnomon-rrule/src/iter.rs:81-93

Description

If expand_period consistently returns empty (e.g., a rule that can never produce occurrences), the iterator tries 1000 consecutive periods before giving up. For sub-daily frequencies, this means ~1000 calls to expand_period.

While not a bug, this is a performance concern for malformed or degenerate recurrence rules.

Suggested Fix

Consider a configurable or frequency-aware retry limit, or validate upfront that the rule can produce occurrences.