fix(ffi): preserve aggregate null-handling support

[Amogh-2404]

Which issue does this PR close?

Part of #22331.

Rationale for this change

ForeignAggregateUDF inherits the default supports_null_handling_clause, so producer overrides are lost across the FFI boundary.

What changes are included in this PR?

• Forward supports_null_handling_clause through FFI_AggregateUDF.
• Use first_value as the positive case and sum as the negative case in forced-foreign and dynamic-library tests.

Are these changes tested?

• cargo test -p datafusion-ffi --features integration-tests
• cargo clippy --all-targets --all-features -- -D warnings

Are there any user-facing changes?

The FFI ABI changes. Foreign libraries must rebuild against the new DataFusion version.

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
    Building datafusion-ffi v54.1.0 (current)
       Built [  62.648s] (current)
     Parsing datafusion-ffi v54.1.0 (current)
      Parsed [   0.062s] (current)
    Building datafusion-ffi v54.1.0 (baseline)
       Built [  61.666s] (baseline)
     Parsing datafusion-ffi v54.1.0 (baseline)
      Parsed [   0.064s] (baseline)
    Checking datafusion-ffi v54.1.0 -> v54.1.0 (no change; assume patch)
     Checked [   0.231s] 223 checks: 222 pass, 1 fail, 0 warn, 30 skip

--- failure constructible_struct_adds_field: externally-constructible struct adds field ---

Description:
A pub struct constructible with a struct literal has a new pub field. Existing struct literals must be updated to include the new field.
        ref: https://doc.rust-lang.org/reference/expressions/struct-expr.html
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.49.0/src/lints/constructible_struct_adds_field.ron

Failed in:
  field FFI_AggregateUDF.supports_null_handling_clause in /home/runner/work/datafusion/datafusion/datafusion/ffi/src/udaf/mod.rs:150
  field ForeignLibraryModule.create_first_value_udaf in /home/runner/work/datafusion/datafusion/datafusion/ffi/src/tests/mod.rs:123

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [ 126.224s] datafusion-ffi

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.65%. Comparing base (88365dd) to head (bb1e57e).

Files with missing lines	Patch %	Lines
datafusion/ffi/src/udaf/mod.rs	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23908      +/-   ##
==========================================
- Coverage   80.65%   80.65%   -0.01%     
==========================================
  Files        1093     1093              
  Lines      371619   371637      +18     
  Branches   371619   371637      +18     
==========================================
- Hits       299730   299727       -3     
- Misses      53993    54009      +16     
- Partials    17896    17901       +5     

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