mcp: use rand.Text and slog.DiscardHandler over internal implementation (#773)

Address TODOs in code requiring go 1.24 as minimum version

mcp/logging.go: use slog.DiscardHandler, over local implementation
mcp/util.go: use rand.Text, over local implementation

Fixes #772

mcp/server.go

@@ -7,6 +7,7 @@ package mcp
 import (
 	"bytes"
 	"context"
+	"crypto/rand"
 	"encoding/base64"
 	"encoding/gob"
 	"encoding/json"
@@ -175,7 +176,7 @@ func NewServer(impl *Implementation, options *ServerOptions) *Server {
 	}
 
 	if opts.GetSessionID == nil {
-		opts.GetSessionID = randText
+		opts.GetSessionID = rand.Text
 	}
 
 	if opts.Logger == nil { // ensure we have a logger