Reforms to the Universal Credit standard allowances do not work

[nwoodruff-co]

This is because the rebalancing uplift directly modifies and saves the standard allowance variable values, bypassing their formula.

[MaxGhenis]

Closing as resolved on current main. The underlying bug was fixed in PR #1547 / commits 8408e8a55 and fb86b9fb9, and current main has a dedicated regression test in policyengine_uk/tests/microsimulation/test_uc_standard_allowance_reform.py covering this case.