fix(backport): count ragged array cardinality correctly

[discord9]

Which issue does this PR close?

• GreptimeTeam issue: N/A
• Related upstream issue: cardinality returns incorrect results for ragged nested arrays apache/datafusion#23270
• Backports upstream fix: fix: cardinality returns incorrect results for ragged nested arrays apache/datafusion#23271

Rationale for this change

cardinality inferred rectangular dimensions and multiplied them, producing wrong results for ragged nested arrays. For example, the three regression witnesses returned 2, 6, 0 instead of 3, 3, 2.

What changes are included in this PR?

• Recursively count actual leaf elements in nested list representations.
• Treat null nested lists as contributing zero while preserving null leaf slots as elements.
• Return a controlled error if the u64 total overflows.
• Add focused ragged, nested representation, and null-semantics regression coverage.

Are these changes tested?

• cargo fmt --all -- --check
• cargo test -p datafusion-functions-nested --lib
• cargo test -p datafusion-sqllogictest --test sqllogictests -- array.slt:5393
• git diff --check

Are there any user-facing changes?

Yes. cardinality now returns the correct number of leaf elements for ragged nested arrays. There are no API or signature changes.