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/readme-quickstart.py

@@ -0,0 +1,19 @@
+from mcp.server.fastmcp import FastMCP
+
+
+# Create an MCP server
+mcp = FastMCP("Demo")
+
+
+# Add an addition tool
+@mcp.tool()
+def add(a: int, b: int) -> int:
+    """Add two numbers"""
+    return a + b
+
+
+# Add a dynamic greeting resource
+@mcp.resource("greeting://{name}")
+def get_greeting(name: str) -> str:
+    """Get a personalized greeting"""
+    return f"Hello, {name}!"