Dataset import lag

[leriomaggio]

Importing static dataset module takes a lot of time.

The issue is caused by global dataset constants to be defined in the module actually reading from files.

This issue could be easily fixed by replacing global constants with loading_functions.

[leriomaggio]

For a very super temporary quick fix, we could have definitions like these in
static_source_datasets.py

SOURCE_SHEILDING_LA = pd.read_csv(p("shielded_pop_LA.csv"))

to be replaced by:

def load_shielding_la():
    global p  # I would also get rid of this p, and would rather make the join in each function ;)
    return pd.read_csv(p("shielded_pop_LA.csv"))

SOURCE_SHEILDING_LA = load_shileding_la

so that in static.py then we just add brackets..

LA_SHIELDING = Dataset(
    data=s.SOURCE_SHEILDING_LA(),
    res=DataResolution.LA,
    key_col="la_name",
    key_is_code=False,
    csv_name="LA_shielded_pop_count",
)

(note s.SOURCE_SHEILDING_LA() has now brackets!)