aider: Rename CustomHandler to MultiplexHandler.

# Aider chat conversation:

USER: rename CustomHandler to MultiplexHandler

ASSISTANT: Here are the necessary changes to rename `CustomHandler` to `MultiplexHandler`:

simplelog.go
```go
<<<<<<< SEARCH
	ourCustomHandler = NewCustomHandler()
=======
	ourCustomHandler = NewMultiplexHandler()
>>>>>>> REPLACE
```

simplelog.go
```go
<<<<<<< SEARCH
type CustomHandler struct {
=======
type MultiplexHandler struct {
>>>>>>> REPLACE
```

simplelog.go
```go
<<<<<<< SEARCH
func NewCustomHandler() slog.Handler {
	cl := &CustomHandler{}
=======
func NewMultiplexHandler() slog.Handler {
	cl := &MultiplexHandler{}
>>>>>>> REPLACE
```

simplelog.go
```go
<<<<<<< SEARCH
func (cl *CustomHandler) Handle(ctx context.Context, record slog.Record) error {
=======
func (cl *MultiplexHandler) Handle(ctx context.Context, record slog.Record) error {
>>>>>>> REPLACE
```

simplelog.go
```go
<<<<<<< SEARCH
func (cl *CustomHandler) Enabled(ctx context.Context, level slog.Level) bool {
=======
func (cl *MultiplexHandler) Enabled(ctx context.Context, level slog.Level) bool {
>>>>>>> REPLACE
```

simplelog.go
```go
<<<<<<< SEARCH
func (cl *CustomHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	newHandlers := make([]ExtendedHandler, len(cl.handlers))
	for i, handler := range cl.handlers {
		newHandlers[i] = handler.WithAttrs(attrs)
	}
	return &CustomHandler{handlers: newHandlers}
}

func (cl *CustomHandler) WithGroup(name string) slog.Handler {
	newHandlers := make([]ExtendedHandler, len(cl.handlers))
	for i, handler := range cl.handlers {
		newHandlers[i] = handler.WithGroup(name)
	}
	return &CustomHandler{handlers: newHandlers}
=======
func (cl *MultiplexHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	newHandlers := make([]ExtendedHandler, len(cl.handlers))
	for i, handler := range cl.handlers {
		newHandlers[i] = handler.WithAttrs(attrs)
	}
	return &MultiplexHandler{handlers: newHandlers}
}

func (cl *MultiplexHandler) WithGroup(name string) slog.Handler {
	newHandlers := make([]ExtendedHandler, len(cl.handlers))
	for i, handler := range cl.handlers {
		newHandlers[i] = handler.WithGroup(name)
	}
	return &MultiplexHandler{handlers: newHandlers}
>>>>>>> REPLACE
```

simplelog.go

@@ -19,17 +19,17 @@ var ourCustomLogger *slog.Logger
 var ourCustomHandler slog.Handler
 
 func init() {
-	ourCustomHandler = NewCustomHandler()
+	ourCustomHandler = NewMultiplexHandler()
 	ourCustomLogger = slog.New(ourCustomHandler)
 	slog.SetDefault(ourCustomLogger)
 }
 
-type CustomHandler struct {
+type MultiplexHandler struct {
 	handlers []ExtendedHandler
 }
 
-func NewCustomHandler() slog.Handler {
-	cl := &CustomHandler{}
+func NewMultiplexHandler() slog.Handler {
+	cl := &MultiplexHandler{}
 	if isatty.IsTerminal(os.Stdout.Fd()) {
 		cl.handlers = append(cl.handlers, NewConsoleHandler())
 	} else {
@@ -52,7 +52,7 @@ func NewCustomHandler() slog.Handler {
 	return cl
 }
 
-func (cl *CustomHandler) Handle(ctx context.Context, record slog.Record) error {
+func (cl *MultiplexHandler) Handle(ctx context.Context, record slog.Record) error {
 	for _, handler := range cl.handlers {
 		if err := handler.Handle(ctx, record); err != nil {
 			return err
@@ -61,25 +61,25 @@ func (cl *CustomHandler) Handle(ctx context.Context, record slog.Record) error {
 	return nil
 }
 
-func (cl *CustomHandler) Enabled(ctx context.Context, level slog.Level) bool {
+func (cl *MultiplexHandler) Enabled(ctx context.Context, level slog.Level) bool {
 	// send us all events
 	return true
 }
 
-func (cl *CustomHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+func (cl *MultiplexHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
 	newHandlers := make([]ExtendedHandler, len(cl.handlers))
 	for i, handler := range cl.handlers {
 		newHandlers[i] = handler.WithAttrs(attrs)
 	}
-	return &CustomHandler{handlers: newHandlers}
+	return &MultiplexHandler{handlers: newHandlers}
 }
 
-func (cl *CustomHandler) WithGroup(name string) slog.Handler {
+func (cl *MultiplexHandler) WithGroup(name string) slog.Handler {
 	newHandlers := make([]ExtendedHandler, len(cl.handlers))
 	for i, handler := range cl.handlers {
 		newHandlers[i] = handler.WithGroup(name)
 	}
-	return &CustomHandler{handlers: newHandlers}
+	return &MultiplexHandler{handlers: newHandlers}
 }
 type ExtendedEvent interface {
 	GetID() uuid.UUID