fix: wrap group_ids OR clause in parentheses for BM25 fulltext query

[giulio-leone]

Summary

Fixes #1249 — BM25 fulltext search with multiple group_ids only filtered by the last group due to missing parentheses around the OR clause.

Problem

Without parentheses, Lucene operator precedence causes AND to bind tighter than OR:

group_id:"1" OR group_id:"2" OR group_id:"3" AND (query)

is parsed as:

group_id:"1" OR group_id:"2" OR (group_id:"3" AND query)

Fix

Wrap the OR clause in parentheses in fulltext_query() (search_utils.py line 101):

# Before
group_ids_filter += ' AND ' if group_ids_filter else ''

# After
group_ids_filter = f'({group_ids_filter}) AND ' if group_ids_filter else ''

Now produces the correct query:

(group_id:"1" OR group_id:"2" OR group_id:"3") AND (query)

Tests

Added tests/utils/search/test_fulltext_query.py with 4 test cases covering single, multiple, no, and empty group_ids.

[danielchalef]

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