feat(query): add HybridQuery for FT.HYBRID server-side fusion

[banker]

Adds HybridQuery and SearchIndex.hybridSearch() that delegate text+vector score fusion entirely to Redis via the FT.HYBRID command (introduced in Redis OSS 8.4.0). Unlike Python redisvl's HybridQuery — which issues two queries client-side and fuses ranks itself — this implementation runs as a single round-trip with server-side RRF or LINEAR fusion.

The new method is separate from index.search() because FT.HYBRID has its own command, options shape, and reply format. HybridSearchResult extends SearchResult with executionTime and warnings fields.

Notable behaviours:

• text + textFieldName triggers tokenize + escape + OR-join. Omitting textFieldName passes the body through verbatim so power users can use full Redis Search syntax.
• vsimFilter is a raw string in the FT.SEARCH filter dialect (e.g. '@brand:{nike}'). postFilter is a raw string in the FT.AGGREGATE expression dialect (e.g. '@price < 200'). The two clauses use different syntaxes server-side.
• LOAD always includes @__key so doc.id round-trips. Score aliases set via YIELD_SCORE_AS are not added to LOAD — Redis already injects them, and re-loading triggers "score alias already exists" errors.
• LOAD/SORTBY field references are auto-prefixed with @ when the user passes bare names; explicit @ or $.path prefixes are preserved.
• Testcontainer image bumped from redis:8.0 to redis:8.4 for FT.HYBRID support.

Marked @experimental in JSDoc since the underlying client.ft.hybrid() is itself flagged experimental in @redis/search.

Tests: 38 unit tests asserting toCommand() output for representative configs (KNN/RANGE methods, RRF/LINEAR fusion, score aliases, LOAD prefixing, SORTBY, NOSORT, postFilter, TIMEOUT) plus 7 integration tests against a real Redis 8.4 Testcontainer covering each fusion method, each vector method, vsimFilter, postFilter, verbatim text body, and LIMIT.

[banker]

Note: latest commit will close #20

[nkanu17]

Addressed the hybrid review pass in b7b087e.
Changes:

• Always emits a default RRF COMBINE with YIELD_SCORE_AS so default HybridQuery results have a stable combined score alias.
• Keeps result mapping defensive by falling back to Redis default score keys if present.
• Adds runtime validation for numResults, offset, timeout, textFieldName, returnFields, sortBy, and noSort/sortBy conflicts.
• Restores the main CI matrix to Redis Stack latest + 7.4.0-v8, and adds a separate Redis 8.4 HybridQuery job for FT.HYBRID coverage.

Verification run locally:

• npm run type-check
• npm run test:unit
• npm test -- tests/integration/hybrid-search.test.ts
• REDISVL_SKIP_HYBRID=true npm test -- tests/integration/hybrid-search.test.ts
• npm run build

[ymendez-redis]

Shall I add the search stopwords or is this not in scope yet?

[ymendez-redis]

Is ommitting stopwords intentionally? redis-vl-python uses NLTK.

[ajGingrich]

Looks like there is an issue for adding separately since TS/Node has no NLTK equivalent

#16

[ymendez-redis]

Nit: the!== ''half of this check is redundant — assertNonEmptyString(config.postFilter, 'postFilter') in the constructor already rejects empty strings. The!==undefined half should stay because the assertion intentionally allows optional fields, and we don't want to emit FILTER = undefined.

[ymendez-redis]

Nit: m.type and m.k is always pre-filled in the constructor and is 10 when not set. No need to add m.k ?? 10 here as this may cause a drift we may not want.

const method = config.vectorMethod ?? { type: 'KNN', k: 10 };