Fix new pedantic lints, disallow implicit casts (dart-lang/pub_semver#40)

- annotate_overrides
- prefer_single_quotes

There is a minor breaking change in `VersionConstraint.unionOf` if any callers
were passing a custom subtype of `VersionConstraint` and _also_ always had
a constraint with `.isAny` of `true`. There are no known remaining callers of
this API and it should be removed - allowing a technically breaking change that
no one will hit allows us to have nice static types within the method.
11 files changed
tree: 9614d04823d71f7bd9e4c1914ad65f96afdacca3
  1. pkgs/