fix: ignore constant aggregate completion boundaries

[yashrb24]

Which issue does this PR close?

• Closes A fixed GROUP BY column is incorrectly used to decide when groups are complete #25018

Rationale for this change

A grouping column with one fixed value never changes, so it cannot tell aggregation that an earlier group is complete.
Currently the logic uses such columns when choosing how aggregation processes its input. This can select the ordered path even when the remaining grouping columns are not ordered.

What changes are included in this PR?

• Ignore fixed grouping columns when deciding when groups can be completed.
• Preserve ordered aggregation when all grouping columns that can change are ordered.
• Update relevant plans

What is the testing strategy for this PR?

Added tests for a grouping column fixed by a filter. The tests fail without the fix.

Are there any user-facing changes?

No query results or public APIs change. DataFusion now chooses the appropriate aggregation path for fixed grouping columns.

[yashrb24]

Since #24697 is making the broader fix for this problem, we can possibly have it fixed in that PR instead of here

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.92683% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.69%. Comparing base (46bbf0d) to head (037c8cf).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/physical-plan/src/aggregates/mod.rs	82.92%	2 Missing and 12 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25019      +/-   ##
==========================================
- Coverage   81.70%   81.69%   -0.01%     
==========================================
  Files        1127     1127              
  Lines      416001   416081      +80     
  Branches   416001   416081      +80     
==========================================
+ Hits       339902   339937      +35     
- Misses      56125    56153      +28     
- Partials    19974    19991      +17     

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