Using `mcp.StdioTransport{}` breaks code coverage reporting during tests

[michaelmcdonnellmw]

Describe the bug

Using mcp.StdioTransport{} for the server transport protocol causes os.Stout to be closed when the server is stopped which prevents go test code coverage from being reported:

$ go test -coverprofile cover.out ./...
error generating coverage report: write /dev/stdout: file already closed

To Reproduce

Create the following main and test files:

package main

import (
	"context"
	"time"

	"github.com/modelcontextprotocol/go-sdk/mcp"
)

func main() {
	RunServer()
}

func RunServer() {
	impl := &mcp.Implementation{}
	options := &mcp.ServerOptions{}
	server := mcp.NewServer(impl, options)

	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
	defer cancel()

	server.Run(ctx, &mcp.InMemoryTransport{})
}

package main

import "testing"

func Test_RunServer(t *testing.T) {
	RunServer()
}

Then run the following to test the code:

$ go test -coverprofile cover.out ./...

Expected behavior

Coverage should be reported and the tests shouldn't fail

$ go test -coverprofile cover.out ./...
ok      mcp-test        0.114s  coverage: 87.5% of statements

[findleyr]

Hi, we probably don't need to close stdin/stdout.

But for testing the SDK, we only run the StdioTransport in a subprocess, using fork+exec.
For most user tests, you can use in-memory transports (mcp.NewInMemoryTransports). Does that solve your problem?

We also just recently added an IOTransport (see #444), which is more flexible.

[findleyr]

Well, we DO need to close stdin to unblock the goroutine reading from it. However, we don't need to close stdout. I'll revert that.

But generally speaking, for tests you should be using mcp.NewInMemoryTransports.