H17: USPS canonical drift

[aks129]

Builds on H16 (requires geocoded output). Compare NDH address to the USPS-canonical address the Census Geocoder returned.

Scope

• % where suite-unit differs (Suite A vs Suite 100) — flag 'likely_same'
• % where ZIP+4 differs
• % where street-direction (N vs North) differs
• % where city differs (subdivision renaming)

Acceptance

• analysis/h17_usps_drift.py
• New finding slug
• Methodology notes call out the 'likely_same' classification rule