refactor: update notification services to use AUS preferences for feature announcements

[baptiste-marchand]

Explanation

Related PR discussion: MetaMask/metamask-mobile#30106 (comment)

References

Fixes: https://consensyssoftware.atlassian.net/browse/GE-244

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Changes the gating logic for fetching feature-announcement notifications to rely on AUS marketing.inAppNotificationsEnabled, which could alter when users see announcements if preferences are missing or inconsistent. Scope is limited to notification fetching behavior and associated tests/changelog updates.

Overview
Feature announcement fetching in fetchAndUpdateMetamaskNotifications now depends on AUS notification preferences (marketing.inAppNotificationsEnabled) rather than the controller’s isFeatureAnnouncementsEnabled state, and it reuses a single preferences read for both announcements and on-chain notification address selection.

Tests were updated to mock AUS marketing preference and assert announcements are fetched/not fetched accordingly, and the changelog documents the switch away from the deprecated controller flag.

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[samir-acle]

LGTM