DeepXDE v1.12.1

Areas of improvement

• Add clear() for forward-mode autodiff to prevent memory leak
• Tensorflow 1.x backend: DeepONet supports layer-by-layer dropout rate setting
• Bug fix: SingleOutputStrategy has unnecessary error checking

New APIs

• dde.geometry.Hypercube supports uniform_boundary_points

Thanks to all the contributors to this release!

@vl-dud @Yiii9 @MinZhu123 @lululxvi @HydrogenSulfate