A rigid flywheel mounted on a frictionless axle is initially at rest at time \(t = 0\). For \(t \ge 0\), a net torque \(\tau(t) = \beta t - \gamma t^2\) is exerted on the flywheel, where \(\beta\) and \(\gamma\) are positive constants. Which of the following expressions represents the maximum angular momentum achieved by the flywheel?