ensmallen 3.11.0: "Sunny Day"

Released Dec. 16, 2025.

• Refactor GradientDescent into GradientDescentType<UpdatePolicyType, DecayPolicyType> and add the DeltaBarDelta and MomentumDeltaBarDelta optimizers (#440).

• Fix an off-by-one bug where the actual number of executed iterations was one fewer than the specified maxIterations (#443).