Tests to verify compatibility will come with a subsequent patch.

The existing `nodes stake` command is not very user-friendly for the
following reasons:
- Need to specify a subcommand custodial or non-custodial
- Need to specify `isBefore8.0` parameter
- Unclear about which wallet signs a message

It's time to introduce a new stake command that is aligned with the
latest node structure.

…tial loss

This patch fixes the following tests:
- TestValidators_String
- TestDefaultParams/Default_Test
- TestValidateGenesis/Test_ValidateGenesis_8
  This test expected a failure in validation because `GetParams`
  returned 50 for `MinSignedPerWindow`, but that bug was fixed.
  The expected result is a success now.

and disabled `TestRPC_QueryUnconfirmedTxs` that was flaky.  It
passed on a local environment, but sometimes failed on GitHub CI.