test: add regression coverage for terminal hash aggregate drain

[hhhizzz]

Which issue does this PR close?

• Closes Add integration regression test for terminal hash aggregate drain #24849.

Rationale for this change

#23182 fixed a performance regression in terminal hash aggregate output by avoiding repeated destructive EmitTo::First calls. However, the remaining MaterializedAggregateOutput unit test only exercises the slicing helper and does not verify the behavior through AggregateExec.

A result-only integration test would pass with both the regressed and fixed implementations, while a wall-clock assertion would be unreliable in CI. This PR therefore uses a test GroupsAccumulator that returns an error if terminal output falls back to destructive EmitTo::First.

What changes are included in this PR?

• Adds single_grouped_aggregate_avoids_destructive_terminal_drain, which runs unordered Single hash aggregation with more groups than the configured batch_size.
• Verifies that AggregateExec selects SingleHash, emits multiple bounded batches, and returns the correct aggregate results for repeated group keys.
• Extends the test accumulator with preserving evaluation and state support so the regression test remains compatible with future direct blocked or chunked output implementations.
• Keeps the test independent of MaterializedAggregateOutput; Single and Final hash aggregation exercise the same terminal drain helper.

What is the testing strategy for this PR?

• Verified that temporarily restoring destructive EmitTo::First(batch_size) causes the new test to fail with the expected accumulator error, while the current implementation passes.
• Applied an equivalent FinalHash accumulator oracle to the historical regression: it fails on d58e0c6d4^ and passes on d58e0c6d4. The migrated SingleHash stream did not exist at that historical revision.
• Ran cargo fmt --all.
• Ran cargo clippy --all-targets --all-features -- -D warnings.
• Ran the extended workspace test suite with avro,json,backtrace,extended_tests,recursive_protection,parquet_encryption; all tests passed after initializing the required Arrow and Parquet test fixtures.

Are there any user-facing changes?

No. This PR only adds regression test coverage.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.55556% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.59%. Comparing base (07483c1) to head (3a614fd).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/physical-plan/src/aggregates/mod.rs	55.55%	25 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24853      +/-   ##
==========================================
+ Coverage   81.58%   81.59%   +0.01%     
==========================================
  Files        1123     1123              
  Lines      408215   408970     +755     
  Branches   408215   408970     +755     
==========================================
+ Hits       333034   333705     +671     
- Misses      55613    55653      +40     
- Partials    19568    19612      +44     

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