Add pytorch model demos(port from tt-forge-fe) & add tt-forge-models as submodule

Author: kamalrajkannan78

.gitmodules

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+[submodule "third_party/tt_forge_models"]
+	path = third_party/tt_forge_models
+	url = https://github.com/tenstorrent/tt-forge-models.git

demos/tt-forge-fe/cnn/efficientnet_demo.py

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+# SPDX-FileCopyrightText: © 2025 Tenstorrent AI ULC
+# SPDX-License-Identifier: Apache-2.0
+
+# Efficientnet Demo Script
+
+import forge
+from ....third_party.tt_forge_models.efficientnet.pytorch import ModelLoader
+
+# Load model and input
+model = ModelLoader.load_model()
+inputs = ModelLoader.load_inputs()
+
+# Compile the model using Forge
+compiled_model = forge.compile(model, sample_inputs=[inputs])
+
+# Run inference on Tenstorrent device
+output = compiled_model(inputs)
+
+# Post-process the output
+# ModelLoader.print_cls_results(output)