v0.2.0 of dewbead

Pure-Dart parser for dewbead schedule documents — turns dewdrop model output into structured, timezone-safe ParsedEvents. No runtime dependencies. Changelog excerpt: - Rewrite to the dewbead v2 format. Breaking. - datetime split into date_part+ optional /time_part. - Anchors carry their unit: t(day), w(week, weekday required), mo(month, day required); ISO absolute dates unchanged. - nis now a relative /time_part(from-now), valid only on tat offset 0. - Endpoints unified to duration | datetime; clock-only inheritance and the midnight-rollover correction are removed (end dates are always explicit). - Multi-record documents via `[...]