Allow multiple NWPs

[dfulu]

Pull Request

Description

Port over changes to datapipes to use multiple NWPs #openclimatefix/ocf_datapipes#254

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (fc82c92) 50.64% compared to head (3737e48) 50.85%. Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #102 +/- ## ========================================== + Coverage 50.64% 50.85% +0.20% ========================================== Files 26 26 Lines 1712 1701 -11 ========================================== - Hits 867 865 -2 + Misses 845 836 -9 ```

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