Improve address ordering for addresses like 11A Foo Street

[chris48s]

example:

ideally this snipped should be sorted

3A, 4A, 11, 11A, 12, 13, 14, 15, 18A, 18B

(without breaking the other various cases we're trying to handle).

At the moment we only split text/numeric components when they're separated by space or comma:

uk-geo-utils/uk_geo_utils/helpers.py

Line 184 in e306348

if len(lst) > 1 and isinstance(lst[0], int) and isinstance(lst[1], str) and (lst[1][0].isspace() or lst[1][0] == ','):

How could we split a string like this intelligently without splitting the entire address into individual characters?