Implement Open Source edition limits and feature restrictions

- Add 5 mutation types (paraphrase, noise, tone_shift, prompt_injection, custom)
- Cap mutations at 50 per test run
- Force sequential execution only
- Disable GitHub Actions integration (Cloud feature)
- Add upgrade prompts throughout CLI
- Update README with feature comparison
- Add limits.py module for centralized limit management
- Add cloud and limits CLI commands
- Update all documentation with Cloud upgrade messaging

rust/pyproject.toml

@@ -0,0 +1,21 @@
+[build-system]
+requires = ["maturin>=1.4,<2.0"]
+build-backend = "maturin"
+
+[project]
+name = "entropix_rust"
+version = "0.1.0"
+description = "High-performance Rust extensions for Entropix"
+requires-python = ">=3.9"
+classifiers = [
+    "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
+    "Programming Language :: Rust",
+    "License :: OSI Approved :: Apache Software License",
+]
+
+[tool.maturin]
+features = ["pyo3/extension-module"]
+module-name = "entropix_rust"