Ian Manske 523d0bca16
Refactor flatten command (#11017)
# Description
Refactors the `flatten` command to remove a bunch of cloning. This was
down by passing ownership of the `Value` to `flat_value`, removing the
lifetime on `TableInside`, and using `Vec<Record>` in `FlattenedRows`
instead of a pair of `Vec` of columns and values.

For the quick benchmark below, it seems to be twice as fast now:
```nushell
let data = ls crates | where type == dir | each { ls $'($in.name)/**/*' }
timeit { for x in 0..1000 { $data | flatten } }
```
This took 550ms on v0.86.0 and only 230ms on this PR.
But considering that
```nushell
timeit { for x in 0..1000 { $data } }
```
takes 200ms on both versions, then the difference for `flatten` itself
is really 250ms vs 30ms -- 8x faster.
2023-11-10 13:18:02 +01:00
..
2023-11-10 13:18:02 +01:00