fix: Use correct registry when creating calls; Remove usage of derive.chain.getBlock

[emostov]

Closes #384

In #351, I removed the querys api.query.session.validators & api.rpc.getBlock. Additionally I removed BlocksService. extractAuthor. I replaced all of them with api.derive.chain.getBlock, which neatly gave us the authorId in addition to the block. (Opposed to having to use the validators and digest logs to extract the authorId)

However, for some reason none of the Codec objects returned from the derive call have a type registry dated to the call, instead they have what seems to be the most recent type registry. The effect of this is that when we try to create Calls that are not in the most recent metadata we get a call not found error. To solver this issue I have brought back the aforementioned code that I removed and use the type registry attached to the block

I experimented with other options like using the type registry on the block hash passed down from the controller, but that had the same issue. We also can't use the events because we do not guarantee that those will be retrieved (e.g. a non-archive node)

[dvdplm]

However, for some reason none of the Codec objects returned from the derive call have a type registry dated to the call

Should we open an issue here (or on pd.js?) to dig into this further?

[dvdplm]

What does extractAuthor return? If it returns undefined this ternary isn't needed.

Suggested change

	const authorId = sessionValidators
	? this.extractAuthor(sessionValidators, digest)
	: undefined;
	const authorId = this.extractAuthor(sessionValidators, digest);

[emostov]

We just need something so TS does not complain since it knows sessionValidators may be undefined.

[dvdplm]

eew, so you're saying we must do like const authorId = this.extractAuthor(sessionValidators, digest) || undefined; just to appease the compiler? :/

[emostov]

Yeah, but we need to check before we call extractAuthor, because extractAuthor requires that the type of the sessionValidators param be Array<AccountId>. I agree with the compiler here because sending down undefined where only an array is expected could lead to issues at runtime.

[dvdplm]

I see what you mean. But is it not an error if sessionValidators is undefined (or an empty array)? Like, shouldn't we bail before we get here if that's the case?

[TarikGul]

LGTM!