createEncryption method
Creates an encryption service.
Returns NoOpEncryptionService by default.
For encryption at app level, pass a custom EncryptionService to
ChatRegistry.custom.
Implementation
EncryptionService createEncryption() {
if (_customEncryption != null) return _customEncryption;
// Always use NoOpEncryptionService at package level
// Encryption should be implemented at app level if needed
return NoOpEncryptionService();
}