fix: avoid instantiating a logger if provided /dev/null (#24027)

- Adds some additional context to workspace traffic logging
- Fails traffic tests if 0 bytes read from connection

cli/clilog/clilog.go

@@ -104,7 +104,7 @@ func (b *Builder) Build(inv *serpent.Invocation) (log slog.Logger, closeLog func
 
 	addSinkIfProvided := func(sinkFn func(io.Writer) slog.Sink, loc string) error {
 		switch loc {
-		case "":
+		case "", "/dev/null":
 		case "/dev/stdout":
 			sinks = append(sinks, sinkFn(inv.Stdout))