feat: per-client Makefile infrastructure for 4-mode testing

Add per-client Makefiles for C, Python, and Go with:
- CLI mode: Tests --help, arg parsing, syntax validation
- Library mode: Unit tests, import verification
- Integration mode: API contract validation (with credentials)
- Functional mode: Real-world scenario tests

C client:
- 22 library tests (SHA-256, HMAC-SHA256, detect_language)
- Full unsandbox.c implementation with examples

Python client (sync + async):
- Delegates to sync/ and async/ subdirectories
- pytest-based test suites with coverage
- Examples for concurrent execution, streaming

Go client:
- Delegates to sync/ and async/ subdirectories
- go test integration with vet and fmt

Also update detect-changes.sh to detect changes in
both root-level un.* files AND clients/ directory.

clients/python/sync/setup.py

@@ -0,0 +1,41 @@
+"""Setup configuration for unsandbox Python SDK (Synchronous)"""
+
+from setuptools import setup, find_packages
+
+with open("README.md", "r", encoding="utf-8") as fh:
+    long_description = fh.read()
+
+setup(
+    name="unsandbox",
+    version="1.0.0",
+    author="Unsandbox",
+    description="Synchronous Python SDK for unsandbox.com code execution",
+    long_description=long_description,
+    long_description_content_type="text/markdown",
+    url="https://github.com/unsandbox/un-inception",
+    packages=find_packages(where="src"),
+    package_dir={"": "src"},
+    classifiers=[
+        "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
+        "Programming Language :: Python :: 3.11",
+        "Programming Language :: Python :: 3.12",
+        "License :: OSI Approved :: MIT License",
+        "Operating System :: OS Independent",
+    ],
+    python_requires=">=3.8",
+    install_requires=[
+        "requests>=2.25.0",
+    ],
+    extras_require={
+        "dev": [
+            "pytest>=6.0",
+            "pytest-cov>=2.0",
+            "black>=21.0",
+            "flake8>=3.9",
+            "mypy>=0.900",
+        ],
+    },
+)