Remove unused requirements_fast.txt file

[Copilot]

This PR removes the requirements_fast.txt file as it is no longer needed in the repository.

What was removed

The requirements_fast.txt file contained the following dependencies:

streamlit
requests
pandas
plotly

Why this change was made

• The file was not referenced anywhere in the codebase or documentation
• No installation scripts or README files mention this requirements file
• The fast_weather_app.py application exists but doesn't explicitly reference this requirements file
• The dependencies appear to be duplicated or covered by other requirements files in the project

Impact

• No functional impact: No code references this file, so removing it doesn't break any functionality
• Cleaner repository: Reduces confusion about which requirements file to use
• Maintained alternatives: The repository still contains requirements.txt and requirements_web.txt for different application variants

Verification

• Confirmed all Python files maintain valid syntax after removal
• Verified no grep matches for "requirements_fast" in the codebase
• Other requirements files remain intact and functional

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