fix: remove unused imports and f-string prefix

Removed unused pytest import from test_helpers.py and removed
unnecessary f-string prefix from static string in demo script.

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

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

Author: bokelley

examples/test_helpers_demo.py

@@ -38,7 +38,7 @@ async def simplest_example() -> None:
 
         if result.success and result.data:
             print(f"✅ Success! Found {len(result.data.products)} products")
-            print(f"   Protocol: MCP")
+            print("   Protocol: MCP")
             print()
         else:
             print(f"❌ Error: {result.error}")

tests/test_helpers.py

@@ -2,8 +2,6 @@
 
 from __future__ import annotations
 
-import pytest
-
 from adcp.client import ADCPClient, ADCPMultiAgentClient
 from adcp.testing import (
     TEST_AGENT_A2A_CONFIG,