Improve multi-tests

[maurolacy]

Follow-up on the current state of testing.

TODO:

• Update sylvia #146
• Remove Mocks / stub contracts. Replace mocks by the real contracts, and adjust tests.
  • vault: cross_staking_mock
  • vault: local_staking_mock
  • converter: virtual_staking_mock
  • native_staking: local_staking_proxy
• Add missing test cases / improve the state of unit / integration testing. Consumer side contracts in particular lack a good of number of tests.
  • Test virtual-staking reply_rewards #131
  • virtual-staking: Add tests for validator withdrawal and rebalance #132
• Send IBC messages when possible. Perhaps by modifying cw-multi-test so that it doesn't fail on unknown IBC messages, but just log them and ignore them.
• Improve test (through cfg_attr(test, msg(exec))) code. See msg(exec) macro conditional on feature / config hashedone/sylvia#206.
• Improve sudo handling / tests, with new sylvia support for it.

[maurolacy]

Closing as done. Will create follow-up issues for the pending bullet points.