Reject Continuous Columns in CTGAN

• Fixed DPCTGAN regression that was impairing utility
• Bug fix where CTGAN synthesizers could silently use continuous column if called without PytorchDPSynthesizer wrapper.
• Fixed bug in dpsgd synthesizers where final batch was not being counted against budget, potentially causing privacy leak
• Alert caller if continuous column is passed as a categorical column to CTGAN
• Warn if log_frequency for CTGAN is set to unsafe value. Spend a small fraction of epsilon to estimate frequencies for conditional sampling.

Bug fixes

• MWEM allows sampling of arbitrary number of records
• Missing splits now handled correctly
• All synthesizers support numpy or pandas input

Scalar Functions

• Add scalar functions to AST
• Allow GROUP BY to group on complex expressions