Add encryption/decryption functionality for adapter config fields in integration tests

[Copilot]

• Add encryption/decryption methods to TestHarness class
• Implement XOR encryption logic as specified in issue
• Modify changeAdapterConfig to automatically encrypt encryptedNative fields
• Add manual encrypt/decrypt methods for developer use
• Add logging for encrypted/decrypted fields for transparency
• Create tests for the new functionality
• Update changelog with breaking change entry
• Build and test the implementation
• Fix linting issues
• Address review feedback: use obj.encryptedNative instead of loadAdapterCommon
• Address review feedback: add private getSystemSecret method with caching

Changes made:

• Added encryptValue() and decryptValue() public methods to TestHarness class for manual use
• Modified changeAdapterConfig() to automatically encrypt fields listed in adapter's encryptedNative array
• Implemented XOR encryption/decryption using the system config secret as specified in the issue
• Added debug logging when fields are encrypted for transparency
• Created comprehensive tests validating the XOR encryption algorithm
• Updated changelog marking this as a breaking change

Review feedback addressed:

• Changed to use obj.common?.encryptedNative instead of loadAdapterCommon() for better flexibility with different adapter names
• Added private getSystemSecret() method with caching to prevent duplicate system config reads and eliminate code duplication
• Removed unused loadAdapterCommon import

Key Features:

• Automatic encryption of encryptedNative fields during config changes
• Manual encryption/decryption methods for developer use
• Uses system config secret for encryption key with caching
• Symmetric XOR encryption (encrypt and decrypt use same operation)
• Logging shows which fields were encrypted for transparency
• Works with any field names listed in adapter's encryptedNative array

Fixes #671.

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