chore(mix): release 2.2.1

[tilucasoli]

Bumps mix to 2.2.1 and closes out the ## Unreleased changelog section.

Why 2.2.1 and not 2.3.0

Patch was chosen deliberately. The two new features are additive optional parameters and #1063 only deprecates (removes nothing), so nothing here forces a minor by compatibility — the call is to ship these as a patch on the 2.2.0 line.

Changes

• packages/mix/pubspec.yaml — version: 2.2.0 → 2.2.1
• packages/mix/CHANGELOG.md — ## Unreleased → ## 2.2.1, plus entries for the merged changes that had none

Included since 2.2.0

PR	Change
#1073	Gradient shorthand transform parameter
#1072	Blur tileMode across core and protocol
#1063	Styler convenience shorthand deprecations
#1071	Stop animation when a style drops its animation config

Notes

• Dependents pin mix: ^2.2.0, which already admits 2.2.1 — no constraint changes needed.
• mix_protocol carries the other half of the tileMode change (feat(mix): support blur tileMode across core and protocol #1072) and is still at 1.0.0-alpha.0 with no entry for it. Publishing mix alone leaves that side unreleased; worth deciding before this merges.
• Only version/changelog files changed, so melos run gen:build && ci && analyze was not run locally — CI covers it. ./scripts/verify_changelogs.sh packages passes.

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