feat: Calculate non-distinct sum from column statistics when available

[AdamGS]

Which issue does this PR close?

• Closes sum aggregate fn can't evaluate value from statistics #23858.

Rationale for this change

Seems like a valuable optimization for sources that report the sum statistic.

What changes are included in this PR?

Implements Sum::value_from_stats, supporting direct column expressions and cast(col) expressions introduced by type coercion.

Casts direct-column statistics to the aggregate return type so decimal sums use the widened SUM type.

Are these changes tested?

Unit coverage for statistics-backed SUM values and decimal accumulator widening, plus core integration coverage for integer and decimal sums from statistics.

Are there any user-facing changes?

None

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.94118% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.71%. Comparing base (18b1e35) to head (28411d6).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/functions-aggregate/src/sum.rs	92.94%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #23863    +/-   ##
========================================
  Coverage   80.70%   80.71%            
========================================
  Files        1090     1090            
  Lines      370150   370424   +274     
  Branches   370150   370424   +274     
========================================
+ Hits       298746   298998   +252     
- Misses      53598    53611    +13     
- Partials    17806    17815     +9     

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