/{runtime}/transactions: Add heuristic field for "is tx a native token transfer?"

[mitjat]

Resolves https://app.clickup.com/t/866ahv3h0

We cannot know if an evm.Call tx transfers native runtime tokens or not, but we can expose a heuristic that all clients will consume.

This PR adds an is_likely_native_token_transfer field to the runtime tx output, with that heuristic.

[csillag]

As far as I can tell, this makes sense. (But someone with more GO experience should also review this.)

[Andrew7234]

should we add this field to required?

[mitjat]

Maybe. I do have arguments for keeping it optional, but they are relatively weak: 1) We currently just omit it if it's false. 2) It's such an unusual field (in that it's a heuristic, rather than just restructured blockchain contents) that I kinda like keeping the door ajar to removing the field later if desired.

I don't need much of a push to promote it to required later.

[pro-wh]

put this on the list of places to think about if a paratime ever uses multiple denominations in the accounts system

[mitjat]

Yeah :/, I thought about it.
The alternative is to add the requirement that body.amount.Denomination == "", where body is the unstructured JSON column in the DB, and that's a little brittle in its own right. So I just went with the less-code option.

[pro-wh]

description is very detailed. could fall out of sync with implementation. please keep an eye out for changes to the heuristic

[mitjat]

description is very detailed. could fall out of sync with implementation.

I agree. The description does say "This is based on a heuristic, and can change at any time without warning and possibly without updating the documentation."
I added the detailed description because I feel it also give a bit of a rationale for why this field is even desirable (i.e. evm.Call txs with their murky semantics)