Add MobileNetV3 operators support to aidge_onnx

Context

This MR is linked to aidge#299 (closed).

This MR aims to add ONNX operators declaration to support MobileNet-v3 Small. The current ONNX model (https://huggingface.co/qualcomm/MobileNet-v3-Small/resolve/main/MobileNet-v3-Small.onnx) uses two operators not yet implemented in Aidge:

• HardSigmoid
• HardSwish

HardSigmoid - ONNX Framework Implementation

ONNX Framework Files

• hardsigmoid.py (50 lines) - ONNX import converter with attribute handling
• hardsigmoid.py (43 lines) - ONNX export converter with attribute preservation

ONNX Import Architecture

• Attribute Handling: Extracts alpha/beta attributes from ONNX nodes with default values (alpha=0.2, beta=0.5)
• Error Handling: Warns about unsupported attributes and falls back to GenericOperator
• Node Creation: Creates aidge_core.HardSigmoid nodes with proper attribute mapping

ONNX Export Architecture

• Attribute Preservation: Exports alpha/beta attributes to ONNX format using helper.make_attribute
• Node Creation: Creates ONNX HardSigmoid nodes with proper input/output mapping
• ONNX Compliance: Follows ONNX HardSigmoid operator specification

HardSwish - ONNX Framework Implementation

ONNX Framework Files

• hardswish.py (42 lines) - ONNX import converter for HardSwish meta-operator
• hardswish.py (31 lines) - ONNX export converter for HardSwish meta-operator

ONNX Import Architecture

• Meta-Operator Support: Direct import of HardSwish meta-operator without attribute processing
• Fixed Values: ONNX HardSwish uses fixed alpha/beta values (alpha=1/6, beta=0.5) - no attributes exposed
• Error Handling: Warns about unsupported attributes and falls back to GenericOperator
• Node Creation: Creates aidge_core.HardSwish nodes with name preservation

ONNX Export Architecture

• Fixed Values: ONNX HardSwish uses fixed alpha/beta values (no attribute export)
• Node Creation: Creates ONNX HardSwish nodes without custom attributes
• ONNX Compliance: Follows ONNX HardSwish operator specification (opset 14+)

MobileNet-V3-Small in Model Zoo

• Testing unit_tests/test_model_zoo.py

External References

• https://onnx.ai/onnx/operators/onnx__HardSigmoid.html
• https://onnx.ai/onnx/operators/onnx__HardSwish.html