From Retrieval to Structured Results: Aggregation and ORDER BY in Milvus 3.0

What this post added

Introduced Query Aggregation with segment-local state merging for distributed execution, handling MVCC visibility before aggregation. Implemented Search Aggregation with a three-stage execution (ANN search, bounded candidate retention per key, bucket building) and distinct control parameters (`SearchAggregation.size`, `TopHits.size`). Added server-side ORDER BY for both query and search results.