feat(audience-sdk): add tracking_authorization_changed event (SDK-332)

[nattb8]

Summary

game_launch fires once per Init(), so any ATT status change mid-session or via iOS Settings (which restarts the app) is invisible to backends until the next launch. A dedicated tracking_authorization_changed event fills that gap, firing whenever the persisted last-known ATT status differs from the current one.

• Fires at Init (covers iOS Settings flips — the app restarts, Init detects the change against the persisted baseline) and after RequestTrackingAuthorizationAsync resolves
• Properties: previousStatus, newStatus, idfa (authorized + Full consent only, per SDK-331 tier rules)
• Last-observed status persisted to imtbl_audience/att_status; first observation seeds the baseline silently — game_launch already captures initial state

Test plan

• First launch: no tracking_authorization_changed event; game_launch carries attStatus
• RequestTrackingAuthorizationAsync → grant: event fires with previousStatus/newStatus/idfa (Full consent)
• Settings flip (disable ATT → re-enable): event fires on next launch via Init
• Anonymous consent: event fires on authorized transition but no idfa
• EnableMobileAttribution = false or consent None: no event
• All existing tests pass (317/317)

🤖 Generated with Claude Code