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 89.65517% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.71%. Comparing base (eef1017) to head (ed69900).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/functions-nested/src/extract.rs	89.65%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23775      +/-   ##
==========================================
- Coverage   80.71%   80.71%   -0.01%     
==========================================
  Files        1089     1089              
  Lines      368748   368777      +29     
  Branches   368748   368777      +29     
==========================================
+ Hits       297633   297651      +18     
- Misses      53372    53375       +3     
- Partials    17743    17751       +8     

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