fix(ci): cache Swift packages in Codemagic

[Sembauke]

Both Codemagic iOS workflows still cache CocoaPods after the migration to Swift Package Manager. Replace that cache with the shared SwiftPM download cache and mobile-app/build/ios/SourcePackages, where Flutter 3.44.3 directs Xcode's package checkouts. Remove cocoapods: default from both workflows and correct the Dart dependency cache to $HOME/.pub-cache, as documented by Codemagic.

Validation: the updated YAML passes the official Codemagic JSON schema, all workflow scripts pass bash -n, and git diff --check passes. iOS builds and actual cache restoration need verification in Codemagic; a successful initial build must populate the cache before a subsequent run can demonstrate reuse.

References: Codemagic SPM caching, Flutter 3.44.3 package checkout path.

Checklist:

• I have read and followed the contribution guidelines.
• I have read and followed the how to open a pull request guide.
• My pull request targets the main branch of the repo.
• I have tested these changes locally on my machine. (Configuration validation passed; macOS/iOS execution is pending CI.)

Closes #1852