feat: FT.HYBRID support via hybrid_vector_search()

[rbs333]

Summary

Adds FT.HYBRID (server-side text + vector fusion, Redis 8.4+) to the SQL translator via a new hybrid_vector_search() SELECT function, alongside the existing FT.SEARCH / FT.AGGREGATE targets.

SELECT user, job, job_description,
       hybrid_vector_search(
           cosine_distance(job_embedding, :vec),   -- VSIM leg
           fulltext(job_description, 'principles'), -- SEARCH leg
           rrf()                                    -- COMBINE (or linear(alpha => 0.3))
       ) AS hybrid_score
FROM user_simple
WHERE region = 'us-central'                         -- per-leg FILTER
ORDER BY hybrid_score DESC
LIMIT 10

Both legs reuse the functions the package already exposes (cosine_distance / vector_distance / vector_range and fulltext); the third argument selects RRF or LINEAR fusion. The options mirror RedisVL's native HybridQuery. Spec: docs/proposals/ft-hybrid.md.

What changed

• Parser: HybridSearchSpec + hybrid_vector_search() detection (composes the nested leg/fusion functions; full validation).
• Analyzer: HybridSearchAnalysis; resolves leg field types (text leg TEXT, vector leg VECTOR), derives KNN K from LIMIT.
• Translator: new FT.HYBRID command path (SEARCH ... VSIM ... COMBINE ..., LOAD, LIMIT, PARAMS). Empirically verified against redis:8.4: KNN/RANGE precedes FILTER, LOAD fields are @-prefixed, and no DIALECT argument (FT.HYBRID rejects it).
• Executor: runs and parses the hybrid reply; vector bytes are injected only into the PARAMS value (the VSIM $vector stays a parameter reference); clear Redis 8.4 version guard.
• redis-py 8.x compatibility: FT.INFO and the hybrid reply are parsed for both the RESP2 list shape and the redis-py 8.x RESP3 map shape.
• Tests: tests/test_ft_hybrid.py (parser/analyzer/translator/executor + integration on real FT.HYBRID) and dict-reply schema tests. Test Redis image bumped 8.0.2 -> 8.4.

Notes

• Fusion config: RRF constant/window, LINEAR alpha only (beta derived as 1 - alpha, matching HybridQuery), KNN ef_runtime, RANGE radius/epsilon.
• LINEAR exposes alpha only by design; an explicit beta is deferred.
• Companion RedisVL SQLQuery tests + user-guide example are tracked separately (RAAE-1322).

Jira: RAAE-1322

[github-actions]

🚀 PR was released in v0.7.0 🚀