Sync numpy-tutorial with the updated tutorial

[realpython-bot]

Syncs numpy-tutorial/ with the maintenance update of NumPy Tutorial: Your First Steps Into Data Science in Python.

What changed

• requirements.txt: replaced the 2020 full pip freeze (NumPy 1.19.1, Matplotlib 3.3.0, notebook 6.1.4, and 50 transitive pins that no longer install on current Python) with direct pins that match the article's updated dependencies field: numpy==2.5.4, matplotlib==3.11.2, plus notebook==7.6.3 for the README's jupyter notebook step.
• No notebook code changes were needed. None of the notebooks use APIs that NumPy 2 removed.

Article draft: https://realpython.com/pbjt/blog/post/2529/change/
Maintenance card: https://trello.com/c/9Ws9hFuf

Verification

• Fresh Python 3.14 venv from the new requirements.txt.
• Ran all five notebooks end to end with MPLBACKEND=Agg jupyter nbconvert --execute, with no errors. The stored outputs still match apart from random draws in normal.ipynb and JPEG-decoder pixel noise in image_mod.ipynb, so I didn't commit re-executed notebooks.
• ruff@0.14.1 format --check and ruff@0.14.1 check both pass.

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