Add missing Alaska boroughs to county_enum.py (Haines, Petersburg)

[hua7450]

Summary

Two Alaska boroughs are missing from county_enum.py, which prevents correct SNAP utility region mapping:

• Haines Borough (FIPS 02100)
• Petersburg Borough (FIPS 02195)

Both should map to AK_SOUTHEAST per Alaska's FSP-77 SNAP utility region assignments.

Impact

Without these enum entries, households in Haines Borough and Petersburg Borough fall through to the default AK_C (Central) region in snap_utility_region.py, resulting in incorrect SNAP utility allowance amounts.

Files to update

1. policyengine_us/variables/household/demographic/geographic/county/county_enum.py — add:

   HAINES_BOROUGH_AK = "Haines Borough, AK"
   PETERSBURG_BOROUGH_AK = "Petersburg Borough, AK"

2. policyengine_us/variables/gov/usda/snap/snap_utility_region.py — add to AK_SOUTHEAST list:

   "HAINES_BOROUGH_AK",
   "PETERSBURG_BOROUGH_AK",

3. May also need to update FIPS dataset in policyengine_us/tools/geography/ if those FIPS codes are missing.

Reference

• Alaska FSP-77 (SNAP utility region assignments by borough)
• Census Bureau FIPS codes: 02100 (Haines Borough), 02195 (Petersburg Borough)

Found during PR #7726 review.