chore(mix): prepare 2.2.0-beta.4

[leoafarias]

Related issue

None. Release preparation.

Description

Cuts mix 2.2.0-beta.4. The only change since beta.3 is #1016, which corrects variant merge priority.

Changes

• packages/mix/pubspec.yaml: 2.2.0-beta.3 → 2.2.0-beta.4
• packages/mix/CHANGELOG.md: ## Unreleased → ## 2.2.0-beta.4

Release contents:

• Variant merge priority follows declared state dependencies. Priority groups active variants by whether they declare ContextVariant.widgetStateDependencies rather than by whether they are a WidgetStateVariant, so onFocusVisible(...) competes by declaration order instead of always losing to any widget-state variant sharing a property. Variants built on ContextVariant.not(...) move with their inner variant, so onEnabled(...) now outranks an ambient variant such as onDark(...) declared after it.
• Declaration order within a priority group is reliable. Grouping is a stable partition rather than a List.sort, which fell back to an unstable quicksort at 32 elements.

Review Checklist

• Testing: No code change. mix suite verified green on fix(mix): order variant merges by declared state dependencies #1016 before merge.
• Breaking Changes: None. No API change and no migration; see fix(mix): order variant merges by declared state dependencies #1016 for the resolved-styling cases the fix corrects.
• Documentation Updates: CHANGELOG heading dated to the release.
• Website Updates: Not applicable to a version bump.

Additional Information

Publishing is tag-driven — .github/workflows/publish.yml fires on mix-v*. After this merges, mix-v2.2.0-beta.4 needs to be tagged on main to publish to pub.dev. This PR does not tag.

Unrelated pre-existing issue noticed while running melos run verify_version_pubspec_changelog: it fails on mix_winds, whose CHANGELOG (0.0.1-alpha.1) does not match its pubspec (0.1.0-alpha.0). Confirmed identical on main before this branch, and the script does not run in CI, so it does not block this release — but it will need fixing before mix_winds is published.