fix: clear_shrink(0) on rows should reset to original size + single group by fixes in clear_shrink

[rluvaton]

Which issue does this PR close?

None

Rationale for this change

For the Row change: clear_shrink 0 should release all memory and return to the initial size so we can return to a memory footprint that we know we can hold (this was found in #24015)

For the rest of the single group by fixes, the clear shrink left the struct in inconsistent state

What changes are included in this PR?

clear memory in rows and reset forgotten fields

What is the testing strategy for this PR?

Unit tests since for the group by it is not reached by our code but still leave in consistent state and it is a public trait
for the rows, it came from other test start failing in #24015 so I just added unit test here as well

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.65%. Comparing base (9547b09) to head (760ef21).

Files with missing lines	Patch %	Lines
...gregates/group_values/single_group_by/primitive.rs	88.88%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25914      +/-   ##
==========================================
- Coverage   82.65%   82.65%   -0.01%     
==========================================
  Files        1147     1147              
  Lines      446087   446179      +92     
  Branches   446087   446179      +92     
==========================================
+ Hits       368721   368783      +62     
- Misses      54980    55002      +22     
- Partials    22386    22394       +8     

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[kumarUjjawal]

Thank you @rluvaton

left one comment also can you resolve the conflict

[kosiew]

@rluvaton,

Thanks for working on these clear_shrink fixes. I found one remaining issue in the row-backed path that still prevents clear_shrink(0) from returning to the initial memory footprint.

[rluvaton]

@kumarUjjawal @kosiew can you approve? I resolved your comments

[kumarUjjawal]

Thank you @rluvaton

Looks good 👍

Resolved