This adds tests to wallet_z_sendmany that demonstrates conditions
where pool-crossing transfers were not being caught by the privacy
policy checks, which were validating only against the transfer
request rather than the actual transfer selected. This missed
cases where sending funds between unified addresses would reveal
amounts via the turnstile.
Making all privacy policy checks after note selection guards against
this error.
Daira Emma Hopwood
Kris Nuttycombe