Add support for RSA decryption and optimize testing setup

[chamodanethra]

Description

This pull request introduces several significant updates:

1. RSA Decryption Support:

   • Adds a decrypt method for RSA payload decryption utilizing hardware-backed private keys.
   • Introduces parameters such as enableDecryption in AndroidConfig and implements respective native decryption logic for both Android and iOS platforms.
   • Provides new classes (DecryptionOptions and DecryptResult) to support the decryption API.
   • Updates the example application with a decryption demonstration.
   • Includes unit tests to ensure the correctness of the decryption implementation.

2. Testing Setup Optimization:

   • Removes default widget test templates from example applications (banking_app, document_signer, example, passwordless_login).
   • Optimizes import statements across the project.
   • Enables the flutter test command in the main.yml workflow for improved automated testing.

Checklist

• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests that verify my fix or feature.
• New and existing unit tests pass locally with my changes.
• I have made corresponding changes to the documentation.

Additional Context

This pull request enhances both functionality and maintainability, ensuring secure payload handling and improving the overall testing infrastructure across the