Update helium-swift SDK to 4.5.4

[github-actions]

Automated update of helium-swift SDK dependency to version 4.5.4.

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.

---

Note

Low Risk
Routine native dependency and version bump with no application code or public API changes in this repo; residual risk is whatever changed inside helium-swift 4.5.4 itself.

Overview
Bumps the iOS helium-swift native SDK from 4.4.8 to 4.5.4 and releases helium_flutter and helium_revenuecat at 3.3.5.

iOS integration pins are updated in Package.swift and helium_flutter.podspec. The Dart heliumFlutterSdkVersion constant and both packages’ pubspec.yaml versions are aligned, with matching changelog entries. There are no Dart or plugin API changes in this diff—only version and dependency wiring.

^{Reviewed by Cursor Bugbot for commit 64e1ee4. Bugbot is set up for automated code reviews on this repo. Configure here.}