Duplicate paragraph in Unit 1.4 — "Training Integration" and "PyTorch DataLoader" repeat the same text

In units/en/unit1/4.mdx, the **## Training Integration** section (line 138) and the following **### PyTorch DataLoader** subsection (line 141) contain the exact same introductory paragraph about integrating regular and streaming datasets with torch data loaders.
The paragraph appears twice in a row, separated only by the **### PyTorch DataLoader** heading, which reads as a copy-paste artifact in the rendered course page.

**Suggested fix:** remove the duplicated sentence from one of the two locations (e.g., keep the **## Training Integration** intro and drop the repeated line under **### PyTorch DataLoader**, or vice versa) so the subsection flows directly into the code example.