Add client examples for streamable http

[rdmcguire]

It would be useful to have a client example for connecting to a streamable http MCP server. A few items that would be great to include:

• TLS
• Auth / Custom Headers
• Middelware

While my basic usage may be wrong, I couldn't find a way to perform even a basic operation using StreamableClientTransport without adding a RoundTripper to add req.Header.Set("Accept", "text/event-stream,application/json").

This seems like something the client should handle, so perhaps I'm using the package wrong (thus the thought that examples may help).

Here is my current (presumably incorrect) usage, which required the roundtripper to make any calls:

func (a *AIWorkerMCP) TestGitToolHandler(ctx context.Context) (*mcp.CallToolResult, error) {
	client := mcp.NewClient(AIWorkerMCPImpl, &mcp.ClientOptions{})

	session, err := client.Connect(ctx, &mcp.StreamableClientTransport{
		Endpoint:   a.getHost() + "/api/mcp/",
		HTTPClient: customHTTPClient,
	}, nil)
	if err != nil {
		return nil, err
	}
	defer session.Close()

	return session.CallTool(ctx, &mcp.CallToolParams{
		Name: "aiworkermcp-git",
		Arguments: &GitToolArgs{
			Repo:         "git@someremote:somerepo.git",
			SourceBranch: "development",
			TargetBranch: "main",
		},
	})
}

type acceptHeaderRoundTripper struct {
	delegate http.RoundTripper
}

func (rt *acceptHeaderRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	req.Header.Set("Accept", "text/event-stream,application/json")
	return rt.delegate.RoundTrip(req)
}

var customHTTPClient = &http.Client{
	Transport: &acceptHeaderRoundTripper{
		delegate: http.DefaultTransport,
	},
}