chore: fix/update example & integration CI

[techouse]

• fixed integration Flutter example
• migrated Flutter Driver test to integration_test
• updated iOS example
• added iOS integration test
• updated Android example
  • supersedes build(deps): bump com.android.tools.build:gradle from 8.1.2 to 8.4.1 in /flutter_secure_storage/example/android #724
• updated Android integration test
• updated Web example
• updated macOS example

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Addresses comment #719 (comment)

[techouse]

@juliansteenbakker I've made quite a few changes, so please let me know if you have any questions.

[juliansteenbakker]

Thank you!