feat: support load/select parquet files into a single variant column.

[youngsofun]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

example

create table t(data variant, filename string, file_row_number int)
copy into t from (select $1, metadata$filename, metadata$file_row_number from @data/parquet/)

• fixes Feature: support query parquet files as a variant column. #18013, refer to the issue for design

arrow types not supported：Timestamp with timezone，Decimal with neg scale，Time32，Time64, Map with non-str key

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

---

This change is 

[sundy-li]

so $1 from parquet means query all columns into a variant column ?

What if the parquet has only one column?

[youngsofun]

so $1 from parquet means query all columns into a variant column ?

yes

What if the parquet has only one column?

the same：map parquet root record to a variant object

[youngsofun]

this failure in ci seems not related to this pr
https://github.com/databendlabs/databend/actions/runs/15316437392/job/43096139604?pr=18028

0: query result mismatch:
[SQL] select count() from list_stage(location=> '@stage_av') where name like '%_sg%';
[Diff] (-expected|+actual)
-   1
+   6
at tests/sqllogictests/suites/ee/03_ee_vacuum/03_0004_auto_vacuum.test:194

cc @dantengsky

[dantengsky]

this failure in ci seems not related to this pr https://github.com/databendlabs/databend/actions/runs/15316437392/job/43096139604?pr=18028
...

@youngsofun Thanks for letting me know it, fixed (and merged) in #18038