fix: nano contracts enabled string

[andreabadesso]

Acceptance Criteria

• Wallet-service /version endpoint returns nanoContractsEnabled boolean field
• Handles fullnode API bug where field may be string values ('disabled', 'enabled', 'feature_activation') instead of boolean
• Properly maps values: true/'enabled'/'feature_activation' → true, everything else → false
• Includes validation, type definitions, and comprehensive test coverage

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged
• Make sure either the unit tests and/or the QA tests are capable of testing the new features
• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.