Cardinality seems inaccurate

[fulmicoton]

Possibly due to the recent change to use the datasketches crate, our cardinality seems very inaccurate for very small values. (where it should really be exact).

Also for large values, the datasketches crate relies on u32 coupon, harming precision for high cardinalities. <- this made no sense.

[PSeitz]

Sketches should only be used above a certain threshold of values (like in elastic search). The current implementation is missing that.

[fulmicoton]

Possibly due to the recent change to use the datasketches crate, our cardinality seems very inaccurate for very small values. (where it should really be exact).

It seems like the new crate is "doing the right thing": starting with list, promoting to set, and then to sketch.
Merge does the right thing as well.

I added a unit test. The problem was observed on quickwit integration test. We might want to investigate what is happening there.

[fulmicoton]

Made this a quickwit bug, as I could not reproduce on raw tantivy (maybe I did not try hard enough)
quickwit-oss/quickwit#6294

Test showing exact results in tantivy.
https://github.com/quickwit-oss/tantivy/blob/main/src/aggregation/metric/cardinality.rs#L729-L746

[fulmicoton]

the bug has been reported here. apache/datasketches-rust#115