feat: add text_match option to HybridSearchConfig for OR keyword matching

[ankurjindal (ecomlisters)]

Hybrid search builds its keyword query with plainto_tsquery, which ANDs every word. Natural-language questions rarely contain every word of the passage that answers them, so the keyword half often returns no rows and hybrid search quietly becomes vector-only.

This adds HybridSearchConfig.text_match:

• "all" (default): unchanged, uses plainto_tsquery.
• "any": matches documents containing at least one query term, ranked by ts_rank_cd as before.

Any other value raises ValueError when the config is created.

For "any", the terms come from to_tsvector(<tsv_lang>, :fts_query), so stemming and stop words behave exactly as they do for "all". Each term is quoted and cast directly to tsquery. The query stays a bound parameter. The terms are not passed through to_tsquery, because that re-parses them as query syntax: a query containing a URL like example.com/a:b?x=1 would raise syntax error in tsquery.

The GIN index on the TSV column is still used. On a 50,000-row table with aapply_hybrid_search_index(), EXPLAIN ANALYZE of the generated query shows a Bitmap Index Scan on the GIN index for both custom and generic plans. The term list is computed once per query (InitPlan), not per row.

Docs: the hybrid search section of examples/pg_vectorstore_how_to.ipynb documents text_match and corrects the stated tsv_column default (it is ""; init_vectorstore_table names a new column <content_column>_tsv). No execution counts or outputs changed.

Tests

• tests/unit_tests/v2/test_async_pg_vectorstore_search.py:
  • A multi-word query where only one word is in a document: "all" returns no keyword matches, "any" returns the document (with and without a TSV column).
  • A stopword-only query ("how is the") does not error.
  • "third-party vendor's" does not error and matches.
  • Terms containing tsquery operators (a URL, & ! | ( ) ') do not error with "any".
  • The default config matches exactly the rows plainto_tsquery returns.
• tests/unit_tests/v2/test_hybrid_search_config.py: "all" and "any" are accepted; other values raise ValueError.

make test: 767 passed. make lint is clean.

Note: this conflicts with #338 on one line, the from typing import ... import in tests/unit_tests/v2/test_async_pg_vectorstore_search.py. Whichever merges second needs the union of both imports.