fix: array_any_value returns NULL for empty list elements

[bjchambers]

Which issue does this PR close?

• Closes array_any_value returns wrong value / panics for empty list elements #23773.

Rationale for this change

array_any_value reads the wrong value (or panics) when its input list column
contains a non-null empty (length-0) element.

general_array_any_value guards null and all-null elements, but a non-null
empty element falls through to the no-nulls branch, which unconditionally reads
values[start]:

• interior empty list → reads values[start], i.e. the next element's
  value (silently wrong data)
• trailing empty list (start == values.len()) → out-of-bounds slice →
  panic range end index N out of range for slice of length N-1

The panic is easy to trigger in practice when the array_any_value output flows
into a hash RepartitionExec (e.g. the value is used as an equi-join key):
repartitioning slices batches so an empty element can land at the end of a
values buffer, tripping the out-of-bounds read on a spawned task.

What changes are included in this PR?

Guard the empty case explicitly in general_array_any_value — an empty list has
no value to take, so the result is NULL.

Sibling functions in extract.rs were audited and are already safe:
array_element bounds-checks the index against len; array_slice /
array_pop_front / array_pop_back guard len == 0.

Are these changes tested?

Yes:

• Kernel-level regression tests for general_array_any_value: an interior empty
  element (previously wrong value) and a trailing empty element (previously
  panic).
• array_any_value.slt cases covering List and LargeList with interior and
  trailing empty elements.

Are there any user-facing changes?

array_any_value now returns NULL for an empty list element instead of
returning the next element's value or panicking the query. No API changes.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.72%. Comparing base (eef1017) to head (7b93d47).
⚠️ Report is 37 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/functions-nested/src/extract.rs	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23775      +/-   ##
==========================================
+ Coverage   80.71%   80.72%   +0.01%     
==========================================
  Files        1089     1090       +1     
  Lines      368748   369362     +614     
  Branches   368748   369362     +614     
==========================================
+ Hits       297633   298170     +537     
- Misses      53372    53419      +47     
- Partials    17743    17773      +30     

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[neilconway]

Overall looks good! Nicely targeted fix, good test coverage.

Can you update the comment that describes array_any_value to document that it returns NULL for empty arrays? (~extract.rs:84).

[bjchambers]

Overall looks good! Nicely targeted fix, good test coverage.

Thanks for the quick review!

Can you update the comment that describes array_any_value to document that it returns NULL for empty arrays? (~extract.rs:84).

This and other comments have been addressed.

[Jefffrey]

we'll need to regenerate function docs via ./dev/update_function_docs.sh