Internally process the request kwargs to optimize caching #208

Is your feature request related to a problem? Please describe.

The following snippet triggers 2 requests from the CDS, although the only difference in the requests is the order of the variables requested.

import earthkit.data
from earthkit.data import settings

settings.auto_save_settings = False
settings.set("cache-policy", "temporary")

request_kwargs = {
    "product_type": "reanalysis",
    "area": [50, -10, 40, 10],  # N,W,S,E
    "grid": [2, 2],
    "date": "2012-05-10",
    "time": "12:00",
}
for reverse in (True, False):
    earthkit.data.from_source(
        "cds",
        "reanalysis-era5-single-levels",
        variable=sorted(["2t", "msl"], reverse=reverse),
        **request_kwargs
    )

Describe the solution you'd like

Internally process the request kwargs to optimize caching.
For example, sort lists (all but area/grid), squeeze single element lists (or do the opposite), change types when possible, ...

Describe alternatives you've considered

No response

Additional context

No response

Organisation

B-Open / CADS-EQC