Avoid cloning in TreeNode.children_nodes() implementations where possible using Cow

[peter-toth]

Avoid cloning in TreeNode.children_nodes() implementations where possible using Cow

[viirya]

Although there is test failure:

SELECT TIMESTAMPTZ '2022-01-01 01:10:00 America/Los_Angeles' as ts_geo
[Diff] (-expected|+actual)
    2021-12-31T14:10:00Z
-   2021-12-31T19:10:00Z
+   2021-12-31T18:10:00Z
    2021-12-31T23:10:00Z
    2022-01-01T09:10:00Z
at test_files/timestamps.slt:1730

But I cannot reproduce it locally. Maybe it is flaky or due to forked repo setting? 🤔 Seems an unrelated failure.

[peter-toth]

Although there is test failure:

SELECT TIMESTAMPTZ '2022-01-01 01:10:00 America/Los_Angeles' as ts_geo
[Diff] (-expected|+actual)
    2021-12-31T14:10:00Z
-   2021-12-31T19:10:00Z
+   2021-12-31T18:10:00Z
    2021-12-31T23:10:00Z
    2022-01-01T09:10:00Z
at test_files/timestamps.slt:1730

But I cannot reproduce it locally. Maybe it is flaky or due to forked repo setting? 🤔 Seems an unrelated failure.

Oh, I didn't notice the failures.
But, that's weird. I don't see them locally either.
And there is this clippy error too:

error: unused import: `exec_err as _exec_err`
   --> datafusion/common/src/error.rs:561:9

but I didn't touch that file.

[viirya]

Let me merge this first and see how CI works in DataFusion repo.