[Test] Added first draft of shape inference test and onnx model in data path...

[Test] Added first draft of shape inference test and onnx model in data path with one custom and one standard node

src/finn/data/onnx/mixed-model/mixed_model.onnx

+onnx-example:

++
+
v
+
+thresholdsout0"MultiThreshold:finn
+
+out0out1"Relu
+test-modelZ
+
v
+

+
+
+
+Z
+
+thresholds
+

+
+b
+out1
+

+
+
+
+j
+out0
+

+
+
+
+B
\ No newline at end of file

tests/test_infer_shapes.py

+from pkgutil import get_data
+
+import numpy as np
+import onnx
+import onnx.numpy_helper as np_helper
+
+import finn.core.onnx_exec as oxe
+import finn.transformation.infer_shapes as si
+from finn.core.modelwrapper import ModelWrapper
+
+
+def test_infer_shapes():
+    # load the onnx model
+    raw_m = get_data("finn", "data/onnx/mixed-model/mixed_model.onnx")
+    model = ModelWrapper(raw_m)
+    model = model.transform_single(si.infer_shapes)
+