feat: Refactoring - Two-Phase Execution Framework

[litedatum]

1. Refactor _decompose_schema_payload() to separate schema and other rules
2. Implement SchemaPhaseExecutor class for phase 1 coordination
3. Implement DesiredTypePhaseExecutor class for phase 2 coordination
4. Create ResultMerger class for combining phase results
5. Add comprehensive logging for debugging two-phase execution
6. Update all test cases to work with new architecture
7. Create performance benchmarks for regression testing

Resolved #38