[perf] optimise key index

[chrispanag]

There are two avenues for optimisation here:

1. There is no need for a reversal and subsequently a copy of the original oplog.values array since this can be handled by a reverse for loop.
2. Mainly, the handled value instead of being an array it can be an object, resulting in O(1) searches for handled values, instead of having to run a linear search each time an oplog value is added (which actually makes the creation of the index O(1/2 n^2 (n + 1)) - Ι think...)

[tabcat]

looks great, thanks for opening this. if you could remove the ; semi-colons to match our standard code style that would be great.

[tabcat]

with 1.0 i want to make sure payload is always defined but this is fine for now, all store indexes are are like this atm.

[chrispanag]

looks great, thanks for opening this. if you could remove the ; semi-colons to match our standard code style that would be great.

Thanks for merging! Adding some prettier rules would be also nice to enforce these code style rules.

[tabcat]

Adding some prettier rules would be also nice to enforce these code style rules.

Yes, in the main repo we have some eslint rules in the package. this package may eventually be a part of the main repo with the other stores and orbit-db-store.