feat: support SELECT DISTINCT id FROM t ORDER BY id LIMIT n query use GroupedTopKAggregateStream

[haohuaijin]

Which issue does this PR close?

close #19638

Rationale for this change

see issue #19638

What changes are included in this PR?

1. Introduced LimitOptions struct limit field with both limit and optional descending ordering direction
2. Extended TopKAggregation optimizer rule to DISTINCT queries by recognizing GROUP BY queries without aggregates and setting the descending flag based on ordering direction
3. Enhanced GroupedTopKAggregateStream to handle DISTINCT by using group key as both priority queue key and value for DISTINCT operations
4. Updated Proto definitions to add optional descending field to AggLimit message for serialization/deserialization

benchmark result

Are these changes tested?

yes, add test case in aggregates_topk.slt

Are there any user-facing changes?

no