internal/mcp: add more package documentation, examples

Add more documentation for the mcp package, explaining how to create and
use Clients and Servers. Also add an example of using the SSEHandler to
crete an MCP server.

Change-Id: Ib327826b2cdb1e3418482551c65569ec6f01af33
Reviewed-on: https://go-review.googlesource.com/c/tools/+/668715
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Neal Patel <nealpatel@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>

mcp/example_test.go

@@ -1,53 +0,0 @@
-// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file.
-
-package mcp_test
-
-import (
-	"context"
-	"fmt"
-	"log"
-
-	"github.com/modelcontextprotocol/go-sdk/mcp"
-)
-
-type SayHiParams struct {
-	Name string `json:"name" mcp:"the name to say hi to"`
-}
-
-func SayHi(ctx context.Context, cc *mcp.ClientConnection, params *SayHiParams) ([]mcp.Content, error) {
-	return []mcp.Content{
-		mcp.TextContent{Text: "Hi " + params.Name},
-	}, nil
-}
-
-func ExampleServer() {
-	ctx := context.Background()
-	clientTransport, serverTransport := mcp.NewLocalTransport()
-
-	server := mcp.NewServer("greeter", "v0.0.1", nil)
-	server.AddTools(mcp.MakeTool("greet", "say hi", SayHi))
-
-	clientConnection, err := server.Connect(ctx, serverTransport, nil)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	client := mcp.NewClient("client", "v0.0.1", nil)
-	serverConnection, err := client.Connect(ctx, clientTransport, nil)
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	content, err := serverConnection.CallTool(ctx, "greet", SayHiParams{Name: "user"})
-	if err != nil {
-		log.Fatal(err)
-	}
-	fmt.Println(content[0].(mcp.TextContent).Text)
-
-	serverConnection.Close()
-	clientConnection.Wait()
-
-	// Output: Hi user
-}