Fix GroupValues retained memory accounting

[kosiew]

Which issue does this PR close?

• Part of feat: analyze memory usage for size functions #23393

Rationale for this change

GroupValues::size() can underreport memory retained by group-value state. In particular, the owner descriptors are not consistently included, and the column-based implementation does not account for several retained allocations used for collision handling, emit scratch space, and vectorized operations.

This can make aggregate memory accounting lower than the memory actually retained by GroupValues, including after reusable buffers have been cleared or groups have been emitted.

This PR updates the accounting so each GroupValues implementation reports its owner descriptor and owned retained allocations exactly once, using allocation capacity where appropriate.

What changes are included in this PR?

This PR:

• Includes the owner descriptor in GroupValuesPrimitive, GroupValuesRows, and GroupValuesColumn memory accounting.
• Includes concrete boxed GroupColumn owner descriptors in their size() implementations.
• Updates row-backed accounting to avoid double-counting inline Rows and RowConverter descriptors.
• Accounts for the GroupValuesColumn allocation backing its group-column collection.
• Accounts for retained group-index lists, including their nested allocations.
• Accounts for the emit group-index scratch buffer.
• Adds accounting for vectorized-operation buffers, including retained capacity after they are cleared.
• Continues to account for reusable buffers by capacity rather than logical length.
• Adjusts two aggregate spill-test memory limits to accommodate the corrected memory accounting.

Are these changes tested?

Yes. This PR adds focused regression tests covering:

• Empty and grown GroupValuesPrimitive memory accounting.
• Empty and grown GroupValuesRows memory accounting.
• Retained row and hash buffers across emit and subsequent reuse.
• Boxed primitive and row-backed GroupColumn owner descriptors.
• Collision group-index lists, emit scratch storage, and vectorized-operation buffers in GroupValuesColumn.
• Retained vectorized and emit scratch capacity after buffers are cleared.

The tests compute expected sizes from the relevant owner descriptors and retained allocations rather than relying on global allocator measurements.

Are there any user-facing changes?

There are no API changes.

Aggregate memory accounting is more complete, so workloads using these GroupValues implementations may report or reserve more memory than before. This can affect when memory limits cause aggregation to spill, reflecting memory that was already retained but previously omitted from GroupValues::size().

LLM-generated code disclosure

This PR includes LLM-generated code and comments. All LLM-generated content has been manually reviewed.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.51477% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.94%. Comparing base (6263df2) to head (a57639a).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
.../src/aggregates/group_values/multi_group_by/mod.rs	95.58%	0 Missing and 6 partials ⚠️
...n/physical-plan/src/aggregates/group_values/row.rs	89.28%	0 Missing and 6 partials ⚠️
...gregates/group_values/single_group_by/primitive.rs	93.75%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25188      +/-   ##
==========================================
+ Coverage   81.91%   81.94%   +0.02%     
==========================================
  Files        1132     1133       +1     
  Lines      421280   423753    +2473     
  Branches   421280   423753    +2473     
==========================================
+ Hits       345111   347248    +2137     
- Misses      55767    55900     +133     
- Partials    20402    20605     +203     

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