feat: multiple columns in count distinct

[Mark1626]

Which issue does this PR close?

Closes #5619

What changes are included in this PR?

1. Introduce a separate accumulator for multi column distinct count MultiColumnDistinctCountAccumulator
2. I used some parts of Count distinct support multiple expressions #5939 for reference, however it was old so I had to reimplement this

Are these changes tested?

1. Unit tests have been added
2. I've tested this with a couple of queries in the cli

with data AS (
  select * from (values
    ('a', 1, 'x'),
    ('a', 2, 'x'),
    ('b', 2, 'y'),
    ('b', 2, 'z'),
    ('c', 3, 'z')
  ) AS t(col1, col2, col3)
)
select count(distinct (col1, col2)) FROM data;

[Dandandan]

Probably https://docs.rs/arrow-row/latest/arrow_row/struct.Row.html or some custom hashing/equality would be much faster than Vec<ScalarValue> as key.

[comphead]

please have tests in .slt

[comphead]

Thanks @Mark1626 for driving this 💪

Before going to code review lets expand tests a little bit to support possible cases, specifically:

• mixed nulls in values
• different column datatypes
• 3+ cols
• different col order
• duplicates like select count(distinct a, a), select count(distinct a, a, b, b)`

Once we have tests passed, we most likely got the code is stable and ready for review

[Mark1626]

@comphead Sure I'll expand the tests, should all these new one be in .slt?

@Dandandan I'll try using struct.Row, I was wondering how I can improve performance

[jonathanc-n]

Does sliding accumulator support distinct on multi column? We should add a test for it and block if it doesn't work. (ex. count(distinct a, b) over ...)

[jonathanc-n]

same column names will look identical here. we should include original field name or col index to differentiate

[jonathanc-n]

this is not a correct comment, we only expect 4

[jonathanc-n]

Lets import use std::mem::size_of_val