Add extended unit tests for AliasDataFrame including lazy join and error handling

- Added tests for:
  * Circular dependency detection
  * Undefined alias symbols
  * Invalid expression syntax
  * Partial materialization logic
  * Subframe behavior with unregistered references
  * Improved save/load integrity checks with alias mean delta validation
  * Direct alias dictionary comparison after load

Known test failures to be addressed:
- Circular dependency not detected (ValueError not raised)
- Syntax error not caught (SyntaxError not raised)
- Undefined symbol not caught (Exception not raised)
- Partial materialization does not preserve dependency logic
- Subframe alias on unregistered frame does not raise NameError

Author: miranov25