feat: add parity between fast_search keyword argument between vector and FTS searches (#3091)

We don't necessarily need to do this, but one user was confused having
used `fast_search=True` as a keyword argument for vector searches, but
being unable to do so for FTS, even after the most recent changes. I
think this is the only discrepancy in where that is possible.

python/python/tests/test_fts.py

@@ -27,6 +27,7 @@ from lancedb.query import (
     PhraseQuery,
     BooleanQuery,
     Occur,
+    LanceFtsQueryBuilder,
 )
 import numpy as np
 import pyarrow as pa
@@ -920,6 +921,10 @@ def test_fts_fast_search(table):
     assert query.limit == 5
     assert query.columns == ["text"]
 
+    # fast_search should be enabled by keyword argument too
+    query = LanceFtsQueryBuilder(table, "xyz", fast_search=True).to_query_object()
+    assert query.fast_search is True
+
     # Verify it executes without error and skips unindexed data
     results = table.search("xyz", query_type="fts").fast_search().limit(5).to_list()
     assert len(results) == 0