BUG: `full_taxes_and_transfers` tests always pass

[MImmesberger]

Bug description

Because those tests are not supposed to check against specific expected values (but are just end-to-end tests for the TT DAG and its inputs), they don't fit into our current notion of policy_cases.

We should

• put the full_taxes_and_transfers tests in a different directory
• create a test that sets all elements of the policy_environment as TT targets and tries to compute them via the inputs in full_taxes_and_transfers. We should only use input columns that have a corresponding policy_input in the policy environment of that date.