Budget reform contract: catch in-place list edits and scale metadata changes in shared parameters #582

GPT-6.1 Sol's round-4 review of #577 (approved) noted two gaps in module_parameters_unchanged, the run-level check that policyengine-uk's shared parameter state is unchanged after a contract run:

1. Snapshot values are the live objects, so a list-valued parameter changed in place (for example append on a UC capital sources list) compares equal to its own snapshot. Executed by the reviewer on a fresh core tree.
2. Node and scale metadata aren't compared. A scale whose metadata.type changes from single_amount to marginal_amount changes tax-scale class, and the row still passes. Executed likewise.

Follow-up to #576/#577 (Budget CI W1).