Add beginner-friendly evaluation feedback for Python lessons

[NickK21]

Summary

• infers each lesson contract from its referenceTest
• adds learner hints for missing variables, missing functions, near-miss names, wrong values, syntax errors, indentation errors, output mismatches, dataframe mismatches, and runtime fallbacks
• keeps beginner-friendly guidance in Outcome and raw technical diagnostics in Output
• wires structured evaluator data through attempt creation and UI rendering
• adds focused API and client tests for contract inference, hint generation, and Outcome/Output rendering