chore: Squelch "unused code" warning

[neilconway]

Which issue does this PR close?

• N/A

Rationale for this change

$ cargo test -p datafusion-functions-aggregate
[...]
  warning: associated function `from_parts` is never used
     --> datafusion/physical-expr/src/expressions/dynamic_filters/mod.rs:464:8
[...]

Fix this by appropriately gating the compilation of from_parts.

What changes are included in this PR?

• Squelch unused code warning

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.67%. Comparing base (9ab2068) to head (38f5aa8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23924      +/-   ##
==========================================
- Coverage   80.68%   80.67%   -0.01%     
==========================================
  Files        1095     1095              
  Lines      372458   372458              
  Branches   372458   372458              
==========================================
- Hits       300500   300486      -14     
- Misses      54032    54042      +10     
- Partials    17926    17930       +4     

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[Jefffrey]

thanks @neilconway