Bump version to 0.2.0, document the release in CHANGELOG, and tighten
the .pubignore to keep the published package lean.

- `pubspec.yaml`: version 0.1.0 → 0.2.0
- `CHANGELOG.md`: promote [Unreleased] to [0.2.0] - 2026-04-01
- `.pubignore`: exclude `coverage/`, `coverage_fresh/`, `coverage_new/`,
  `coverage_final/`, and `codecov.yml` from the published archive;
  package size drops from 667 KB → 44 KB

Signed-off-by: Joel Winarske <joel.winarske@gmail.com>