refactor: Simplify LimitedDistinctAggregation optimizer rule

[2010YOUY01]

Which issue does this PR close?

This is primarily a simplifying refactor, with an optimizer regression fix piggy-backed on top (an inefficient plan shape, not a correctness issue):

• fix: keep aggregate limits when combining or rebuilding AggregateExec #25983 (comment)

The optimizer fix itself is only a one-line change. If this simplification is not desirable, I'll open a replacement PR containing just the direct fix.

Rationale for this change

Part 1: Optimizer fix

See sqllogictest diff for the reproducer
I'll mark the fix in comments

Part 2: Optimizer simplification

During different stages in physical optimization, a logical aggregation can be either

AggregateExec(mode=final)
--AggregateExec(mode=partial)

AggregateExec(mode=single)

AggregateExec(mode=final)
--RepartitionExec
----AggregateExec(mode=partial)

So the existing implementation is using a nested dfs (the closure has another dfs inside, to match non-consecutive aggregates) try to match all of the 3 cases.

However, after looking at related optimizer rules:

• initial physical planning
• CombinePartialFinalAggregate
• EnsureDistributions
• and this rule

We can find only case 1 is possible, so the implementation can be simplified into a naive pattern matching

Find the exact below shape, and try push limits

LimitExec
--AggregateExec(mode=final)
----AggregateExec(mode=partial)

What changes are included in this PR?

• simplify an optimizer rule according to the above rationale
• fix a small bug

What is the testing strategy for this PR?

• for bug fix, changes in slt
• To ensure refactor correctness: no e2e test need to be changed

Are there any user-facing changes?

[2010YOUY01]

bug fix: missing a as_final to adapt projection difference

[2010YOUY01]

👉🏼

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.57143% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.69%. Comparing base (c3ef346) to head (784d746).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
...ical-optimizer/src/limited_distinct_aggregation.rs	88.57%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26069      +/-   ##
==========================================
+ Coverage   82.66%   82.69%   +0.02%     
==========================================
  Files        1147     1147              
  Lines      446357   447312     +955     
  Branches   446357   447312     +955     
==========================================
+ Hits       368971   369892     +921     
- Misses      54997    55008      +11     
- Partials    22389    22412      +23     

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