refactor: Update FastMCP examples to use new import path

Update all FastMCP examples to use mcp.server.fastmcp instead of fastmcp.
Add tests to verify example servers work correctly.

Changes:
- Update import paths in all example files
- Create test_examples.py to verify functionality
- Fix test assertions to match actual response format

examples/fastmcp/simple_echo.py

@@ -0,0 +1,15 @@
+"""
+FastMCP Echo Server
+"""
+
+from mcp.server.fastmcp import FastMCP
+
+
+# Create server
+mcp = FastMCP("Echo Server")
+
+
+@mcp.tool()
+def echo(text: str) -> str:
+    """Echo the input text"""
+    return text