Add 1991-2020 climate normals

[steffilazerte]

ECCC has released the 2020 climate normals and weathercan should add these to stations() etc.

[steffilazerte]

A couple of things to consider

1. The climate normals are not completely released, as of Nov 2024
2. There is a station inventory for locations with new normals: https://climate.weather.gc.ca/climate_normals/station_inventory_e.html?yr=1991
3. The new normals use composite stations, combining data from several stations in an area (see Section 1.2)
4. The API format for downloading this composite data includes a new station id, which isn't on the current station meta data lists
   • See Download button inputs
   • Nov 2024 - Emailed ECCC normals team for the Prairies to see if I can get a list of station ids. Response: there should be an official way to bulk download these sometime hopefully by February 2025

[mahjabinoyshi]

I’ve opened PR #199 which adds:

• normals_code and normals_1991_2020 columns to stations, based on the 1991–2020 station inventory.
• A data-raw script to regenerate stations from the ECCC inventory.
• Experimental helpers get_normals_1991_2020_stations() and normals_dl_1991_2020() (currently using climate_id as stnID until an official mapping is available).

Happy to revise the approach based on any feedback, especially once the official bulk-download / ID mapping from ECCC is available.