refactor: remove evaluate_logic from public API

Remove evaluate_logic as a public method from both WASM exports and
Python bindings. The project is focused exclusively on flag evaluation
using the stateful update_state + evaluate pattern, not general-purpose
JSON Logic evaluation.

Changes:
- Remove evaluate_logic WASM export function from src/lib.rs
- Remove EvaluationResponse struct (no longer needed)
- Remove evaluate_logic from Python bindings (python/src/lib.rs)
- Update API Reference table in README.md
- Update all usage examples (Python, JavaScript, Rust) to use flag evaluation
- Remove Python examples that demonstrated evaluate_logic
- Remove test_operators.py (tested evaluate_logic)
- Update benchmarks to only test FlagEvaluator
- Remove PYTHON_TODO.md (all tasks completed)
- Clean up unused serde imports

This aligns the implementation with the flagd provider specification
and reduces API surface area.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: aepfli