Add SAM2 models and AI Batch Mode

[jakep72]

• Support for Segment Anything 2 tiny and large models. Models are currently located in the fork release (see below):

SAM2 Large Models
https://github.com/jakep72/labelme/releases/download/SAM2/sam2_large.encoder.onnx
https://github.com/jakep72/labelme/releases/download/SAM2/sam2_large.decoder.onnx

SAM2 Tiny Models
https://github.com/jakep72/labelme/releases/download/SAM2/sam2_hiera_tiny.encoder.onnx
https://github.com/jakep72/labelme/releases/download/SAM2/sam2_hiera_tiny.decoder.onnx

• Implement "AI Batch" mode -- adds the ability to label multiple similar polygons without clicking on each object. Accept or reject each polygon using the label dialog pop up widget.