Fix review findings: ACTION:NONE alarms, negative offsets, non-ASCII UIDs

- valarms()/lead() now skip RFC 9074 ACTION:NONE placeholder VALARMs, so
  those events fall through to the calendar default instead of going silent.
- fmt_duration() renders negative timedeltas as "-Xd Yh Zm" instead of a
  wrapped-around wall-clock artifact.
- save_overrides() writes JSON with ensure_ascii=False and utf-8 encoding,
  so non-BMP UIDs (e.g. emoji) round-trip through tomllib instead of being
  written as surrogate-pair escapes tomllib rejects.

Marked as known limits with ponytail comments (no behaviour change):
- valarms()/alarms_for(): offsets add in wall-clock time, off by the jump
  across a DST transition.
- lead(): absolute DATE-TIME triggers don't widen the expansion window.
- expand(): RDATE is ignored.
- rule_for(): a VEVENT with more than one RRULE line fails and is skipped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions