fix incorrect nested array value

[zhicwu]

Summary

Checklist

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• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[zhicwu]

Will merge tomorrow after benchmarking. The flaky tests on the other will be fixed(or disabled) in a separate PR.

-- works in 0.4.0
select [[1,2],[2,1],[3,4]]::Array(Array(Int8))

-- fixed 0.4.1
select [[1,2],[2,1],[3,4]]::Array(Array(Nullable(Int8)))
select [['aa','bb'],['cc','dd']]::Array(Array(String))
select [[['aa','bb'],['cc','dd']],[['aa2','bb1'],['cc1','dd2']]]::Array(Array(Array(String)))

[zhicwu]

The fix works at the cost of higher memory usage for nested arrays. Also I spotted issue in piped output stream during benchmarking. Should be good to merge this one first and fix other issues in separate PRs.