feat: add comprehensive client library and CI workflow

[BohuTANG]

Summary

• Add UDFClient for simplified UDF server testing
• Implement professional test suite with isolated server instances
• Add comprehensive validation and error handling
• Support both positional and batch function calls
• Update CI workflow to include linting, formatting, and testing across Python 3.9-3.12
• Fix code formatting and linting issues

Test plan

• All 10 tests pass locally
• Code formatting and linting checks pass
• Package builds successfully
• CI workflow runs and passes on GitHub