Data from read_json functions could be stored as constants

I noticed during work on #67 that the read_json functions are called seperately in each AGB disciplines `make_classification_dict` function and stored to locals.

These could be called once and saved as constants, as any change to the data being loaded would require installing an updated version of archeryutils.

Start by locating the read_json functions and each AGB discipline's make_classification_dict function. Review how the loaded data is currently assigned to locals, then identify the existing tests or validation for these functions. Done means the data is loaded once as constants and all classification functions continue to produce the same results.

Written by the indexing model from the issue text.