feat(hybrid): support facets on fused hybrid results

[donhardman]

FACET / aggs in hybrid search (fusion_method='rrf') — closes #4928

CREATE TABLE t (title text, cat int, vec float_vector knn_type='hnsw' knn_dims='4' hnsw_similarity='l2');
INSERT INTO t (id,title,cat,vec) VALUES
 (1,'machine learning basics',1,(0.1,0.1,0.1,0.1)),(2,'deep learning',1,(0.2,0.1,0.1,0.1)),
 (3,'cooking pasta',2,(0.1,0.1,0.1,0.15)),(4,'machine repair',2,(0.9,0.9,0.9,0.9)),
 (5,'gardening',3,(0.5,0.5,0.5,0.5)),(6,'learning to cook',3,(0.8,0.8,0.8,0.8));

SELECT id FROM t WHERE match('learning') AND knn(vec,(0.1,0.1,0.1,0.1)) LIMIT 3
OPTION fusion_method='rrf' FACET cat;

SELECT id, hybrid_score() hs FROM t WHERE match('learning') AND knn(vec,(0.1,0.1,0.1,0.1)) AND hs > 0.02
OPTION fusion_method='rrf' FACET cat;

Before

ERROR 1064 (42000): table t: hybrid search does not support multiple sorters
ERROR 1064 (42000): table t: HYBRID_SCORE() is only allowed for hybrid search queries

JSON aggs in a hybrid /search request failed the same way.

After: facets count all fused documents (not only the LIMIT page), after post-fusion filters:

+------+----------+          +------+----------+
| cat  | count(*) |          | cat  | count(*) |
+------+----------+          +------+----------+
|    1 |        2 |          |    1 |        2 |
|    2 |        2 |          |    3 |        1 |
|    3 |        2 |          +------+----------+
+------+----------+          (hs > 0.02 keeps docs 1, 2, 6)

facet_filter_mode, FILTERS/EXCLUDE FILTERS, GROUP BY, DISTINCT, JOIN, and distributed tables are supported. Test: test/test_537. Manual: Searching → Hybrid search → Facets.