Update helium-swift SDK to 4.5.3

[github-actions]

Automated update of helium-swift SDK dependency to version 4.5.3.

Changes:

• Updated Package.swift dependency version
• Updated podspec dependency version
• Bumped helium_flutter pubspec.yaml version (patch increment)
• Bumped helium_revenuecat pubspec.yaml version (patch increment)
• Updated heliumFlutterSdkVersion constant
• Added changelog entries to both packages

This PR was automatically created by the iOS SDK release workflow.

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Note

Low Risk
Routine dependency pin and semver patch bumps with no application logic changes in the diff; residual risk is whatever changed inside helium-swift 4.5.3 itself.

Overview
Patch release that pins the iOS helium-swift native SDK from 4.4.8 to 4.5.3 and aligns Flutter package versions to 3.3.5.

Updates land in Package.swift and helium_flutter.podspec, plus heliumFlutterSdkVersion and both helium_flutter / helium_revenuecat pubspec.yaml and changelog entries. No Dart or plugin API changes appear in this diff—consumers get the newer native Helium behavior bundled with helium-swift 4.5.3.

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