Return Touched Accounts inside the Spawn and Call Receipts

[YaronWittenstein]

Notes

Before working on this issue, please make sure this one is addressed #406

Details

While calling an existing Account (i.e., executing a Call transaction) and spawning new ones (involves running a constructor), we might transfer coins between different Accounts.

go-spacemesh would like to be notified which accounts were involved in coins transfers as part of executing a transaction.

In other words, each time the svm_transfer host function is being called, we'd like to append the source and destination into the Touched Accounts set.

The logged source will always be the same Address - the currently executing Account.
So the implementation can optimize that, but keeping things simple and stupid in the solution might be a better approach.

The task of the issue is to make sure that Spawn and Call receipts will have a new touched_accounts field that will contain this list of Account Addresses.

Encoding

Lastly, this field should also be encoded in the returned Receipts.

See the svm-codec code here:
https://github.com/spacemeshos/svm/tree/master/crates/codec/src/receipt

[neysofu]

Just clarifying this: "touched accounts" is a set, and as such doesn't make any distinction between source and destination because it's, duh, a set (like std::collections::HashSet). source and destination are out-of-band terms that we use to understand what items should be included in that set. @YaronWittenstein do we agree on this?

[YaronWittenstein]

To my understanding, yes!
It's the list of accounts that have been involved in at least one coins transfer during the transaction execution.

[neysofu]

Nice, we're on the same page then.