only support rows(): AsyncRow[]

[severo]

This PR is a breaking change in the dataframe's rows method, since it must return AsyncRow[], instead of supporting two types: AsyncRow[] | Promise<Row[]>.

Also, I separate the index from the values to avoid collisions and make the code simpler:

type Cells = Record<string, any>

/**
 * A row where each cell is a resolved value.
 */
export interface Row {
  cells: Cells
  index: number
}

[severo]

wdyt @platypii?

The internal code is a bit simpler, I think. But the interface to pass the data is a bit more complex (see the changes in the tests). So... not sure

I feel like wrapPromise and asyncRows are still two ways to do the same and we might simplify this too.

[platypii]

I like this direction. I think that having the __index__ in the same object as the columns was making the code really awkward.

The dataframe interface is okay to be a little complicated especially since we have helpers like asyncRows which can help. There might be some other helpers which could make it easier for a naive implementation (so that down stream users can just have resolved objects and not have to understand asyncrows). But also... no one besides us is using hightable yet, and we should keep evolving it to suit our needs.

[platypii]

Should update the README too

[severo]

OK! I'll update the README and merge.