fix(examples): use CERT_PATH environment variable in client_server examples

Updates Python client scripts to use CERT_PATH environment variable for
certificate paths instead of hardcoded relative paths. This ensures tests
work correctly regardless of working directory.

Changes:
- client.py: Use os.getenv('CERT_PATH') with Path-based fallback
- async_client.py: Use os.getenv('CERT_PATH') with Path-based fallback
- Makefile: Pass CERT_PATH to both client tests

Author: sam

Makefile

@@ -509,9 +509,9 @@ python-example-client-server:
 	@echo "Starting server..."
 	@cd examples/python/client_server && PYTHON=$(VENV_PYTHON) $(VENV_PYTHON) $(ROOT_DIR)/examples/python/client_server/server.py & echo $$! > /tmp/rpcnet_test_server.pid && sleep 10
 	@echo "Running blocking client test..."
-	@cd examples/python/client_server && timeout 60 $(VENV_PYTHON) $(ROOT_DIR)/examples/python/client_server/client.py || (kill $$(cat /tmp/rpcnet_test_server.pid) 2>/dev/null; rm -f /tmp/rpcnet_test_server.pid; exit 1)
+	@cd examples/python/client_server && CERT_PATH=$(ROOT_DIR)/certs/test_cert.pem timeout 60 $(VENV_PYTHON) $(ROOT_DIR)/examples/python/client_server/client.py || (kill $$(cat /tmp/rpcnet_test_server.pid) 2>/dev/null; rm -f /tmp/rpcnet_test_server.pid; exit 1)
 	@echo "Running async client test..."
-	@cd examples/python/client_server && timeout 60 $(VENV_PYTHON) $(ROOT_DIR)/examples/python/client_server/async_client.py || (kill $$(cat /tmp/rpcnet_test_server.pid) 2>/dev/null; rm -f /tmp/rpcnet_test_server.pid; exit 1)
+	@cd examples/python/client_server && CERT_PATH=$(ROOT_DIR)/certs/test_cert.pem timeout 60 $(VENV_PYTHON) $(ROOT_DIR)/examples/python/client_server/async_client.py || (kill $$(cat /tmp/rpcnet_test_server.pid) 2>/dev/null; rm -f /tmp/rpcnet_test_server.pid; exit 1)
 	@kill $$(cat /tmp/rpcnet_test_server.pid) 2>/dev/null || true
 	@rm -f /tmp/rpcnet_test_server.pid
 	@echo "✅ Client/Server example passed"

examples/python/client_server/async_client.py

@@ -2,6 +2,7 @@
 import asyncio
 import sys
 import time
+import os
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).parent / "generated"))
@@ -14,9 +15,12 @@ async def main():
     print("🚀 RpcNet Async Client")
     print("=" * 70)
 
+    # Use environment variable or default relative path
+    cert_path = os.getenv("CERT_PATH", str(Path(__file__).parent.parent.parent.parent / "certs" / "test_cert.pem"))
+    
     client = await BenchmarkServiceClient.connect(
         addr="127.0.0.1:50051",
-        cert_path="../../../certs/test_cert.pem",
+        cert_path=cert_path,
         server_name="localhost"
     )
     print("✅ Connected")

examples/python/client_server/client.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 import sys
 import time
+import os
 from pathlib import Path
 
 sys.path.insert(0, str(Path(__file__).parent / "generated"))
@@ -13,9 +14,12 @@ def main():
     print("🚀 RpcNet Client")
     print("=" * 70)
 
+    # Use environment variable or default relative path
+    cert_path = os.getenv("CERT_PATH", str(Path(__file__).parent.parent.parent.parent / "certs" / "test_cert.pem"))
+    
     client = BenchmarkServiceBlockingClient.connect(
         addr="127.0.0.1:50051",
-        cert_path="../../../certs/test_cert.pem",
+        cert_path=cert_path,
         server_name="localhost",
         timeout_secs=10
     )