Remove duplicates

[peterdudfield]

Pull Request

Description

Occacisioanly there are multe value for target_time, gsp_id, and model_name in the forecast_value_latest. This can happen when we upgrade a model, then the API will provide this duplicates when

• pulling national data with include_data
• non compact for forecast/all.
• but not for all other routes

This PR solves that
Helps solve #450

Speed did not significantly change

How Has This Been Tested?

• CI test
• tested locally

Checklist:

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

[braddf]

Yep, you've already left a comment re this (nowcasting_api/utils.py#L225) so yep although this works, this is another code smell for me that we're having to do these sorts of things on the API side and not in the DB queries, so another one to think about for future