Add partnership_se_income to IMPUTED_VARIABLES

The variable was added to FINANCIAL_SUBSET in puf.py but also needs
to be in IMPUTED_VARIABLES in extended_cps.py to be imputed into the
Enhanced CPS dataset.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MaxGhenis

policyengine_us_data/datasets/cps/extended_cps.py

@@ -51,6 +51,7 @@
     "miscellaneous_income",
     "alimony_expense",
     "farm_income",
+    "partnership_se_income",
     "alimony_income",
     "health_savings_account_ald",
     "non_sch_d_capital_gains",