Accepts partial codes ('541') or keywords ('software'). Returns matching
NAICS entries with code and description.

Minimum 2 characters required. Short queries silently match substrings
inside parenthetical notes (e.g. 'x' matches 'except') and produce
nonsense results, so we require 2+ chars.

exclude_retired defaults to True. The upstream NAICS taxonomy still
returns codes retired in 2012/2017/2022; these are almost never what
callers want. Set exclude_retired=False to include them.