Consolidate computation_modules.py with CountryConfig from policyengine library

[anth-volk]

Problem

computation_modules.py has 818 lines with 13 module functions — many duplicated as _uk/_us variants that differ only in program names, variable lists, and calculator functions. Each module function also:

• Hard-codes country-specific program/variable lists (duplicating what the library should own)
• Calls model_rebuild() workarounds that are now fixed in the library
• Has two separate dispatch tables (UK_MODULE_DISPATCH, US_MODULE_DISPATCH)

Solution

Use CountryConfig from policyengine.outputs.country_config (added in PolicyEngine/policyengine.py#260) to:

• Replace 6 duplicate module functions with single config-driven functions
• Replace two dispatch tables with one MODULE_DISPATCH
• Remove inline program/variable lists (now in US_CONFIG/UK_CONFIG)
• Remove model_rebuild() calls (fixed in library's __init__.py)

Dependencies

• Requires Consolidate economic impact analysis into shared compute functions policyengine.py#260 to be merged first