Update GFS data preprocessing for correct longitude range

[AoufNihed]

Fixes #82

Changes Made

• Modified GFS data preprocessing to handle correct longitude range (-10 to 0 instead of 350 to 360)
• Added constants.py for NWP data normalization values
• Updated gfs_dataset.py to use proper longitude selection for UK region
• Added test cases in test_gfs_dataset.py to verify longitude handling
• Improved error handling and logging in DWD and GFS data processing

Testing

• Added unit tests for GFS data preprocessing
• Verified longitude selection with sample data
• All tests passing locally:
  • black ✅
  • ruff ✅
  • pre-commit hooks ✅

Additional Notes

The current GFS data has longitude values from -10 to 0 for the western UK region, so updated the preprocessing logic to handle this range correctly instead of assuming 350-360 range.

[peterdudfield]

@siddharth7113 would you like to review this?

[siddharth7113]

Hi @AoufNihed , Thank you for opening a PR on the issue, I see a lot of changes might not be related to the issue #82 , I would request you to not make changes to files unrelated to the issue, this would help in reviewing faster.

[AoufNihed]

@siddharth7113 Okay, I will.