This was recently added in neotest, but working with the real RPC is
still not enjoyable. This commit extends `wallet.Account` with
invocation script builder to aid network fee calculations and signing.
Signed-off-by: Evgenii Stratonikov <fyfyrchik@runbox.com>
Everywhere including examples, external interop APIs, bindings generators
code and in other valuable places. A couple of `interface{}` usages are
intentionally left in the CHANGELOG.md, documentation and tests.
Somewhat similar to invoker, but changing the state (or just creating a
transaction). Transaction creation could've been put into a structure of its
own, but it seems to be less convenient to use this way.
