Upgrade breakdown enum mismatch from WARNING to ERROR

[MaxGhenis]

Summary

When a parameter YAML file declares breakdown: [some_enum_variable], the homogenize_parameters function in policyengine-core checks whether the YAML's top-level keys match the enum values. Currently, if a YAML contains keys that are not in the breakdown enum, it only logs a WARNING and keeps the orphaned children — it should raise an ERROR instead.

Problem

In policyengine_core/parameters/helpers/homogenize_parameters.py (around line 109-111), mismatched keys produce a warning like:

WARNING  policyengine_core.parameters.helpers.homogenize_parameters:homogenize_parameters.py:111
Parameter gov.usda.snap.income.deductions.utility.standard.main has children ['AK_C', 'AK_N', ...] that are not in the breakdown variable snap_utility_region

But execution continues, silently dropping or ignoring those keys. This caused real data loss in PolicyEngine/policyengine-us#7726, where SNAP utility allowance parameters had breakdown: [state_code] but used snap_utility_region enum keys (like AK_C, NY_NYC). The sub-region values were silently ignored with only a warning.

Proposed fix

Upgrade the warning to an error (raise an exception) when a parameter YAML contains keys that are not in the breakdown enum.

Important: only flag extra keys not in the enum, not missing enum values. There are legitimate cases where a YAML intentionally omits some enum values:

• state_code breakdown omitting armed forces codes (AA, AE, AP) — no data exists for those
• filing_status breakdown omitting SURVIVING_SPOUSE — IRS SOI data doesn't track it separately

So the validation should be:

• yaml_keys - enum_values is non-empty → ERROR (unknown keys that will be silently dropped)
• enum_values - yaml_keys is non-empty → fine (partial coverage is intentional)

Impact

Without this fix, typos or mismatched breakdown declarations silently discard parameter data, which is very difficult to debug. The current half-state (warn but keep the orphaned children) is confusing and error-prone.