fix(python): Few fts patches (#1039)

1. filtering with fts mutated the schema, which caused schema mistmatch
problems with hybrid search as it combines fts and vector search tables.
2. fts with filter failed with `with_row_id`. This was because row_id
was calculated before filtering which caused size mismatch on attaching
it after.
3. The fix for 1 meant that now row_id is attached before filtering but
passing a filter to `to_lance` on a dataset that already contains
`_rowid` raises a panic from lance. So temporarily, in case where fts is
used with a filter AND `with_row_id`, we just force user to using the
duckdb pathway.

---------

Co-authored-by: Chang She <759245+changhiskhan@users.noreply.github.com>

python/python/tests/test_fts.py

@@ -137,7 +137,11 @@ def test_search_index_with_filter(table):
 
     # no duckdb
     with mock.patch("builtins.__import__", side_effect=import_mock):
-        rs = table.search("puppy").where("id=1").limit(10).to_list()
+        rs = table.search("puppy").where("id=1").limit(10)
+        # test schema
+        assert rs.to_arrow().drop("score").schema.equals(table.schema)
+
+        rs = rs.to_list()
         for r in rs:
             assert r["id"] == 1
 
@@ -147,6 +151,10 @@ def test_search_index_with_filter(table):
         assert r["id"] == 1
 
     assert rs == rs2
+    rs = table.search("puppy").where("id=1").with_row_id(True).limit(10).to_list()
+    for r in rs:
+        assert r["id"] == 1
+        assert r["_rowid"] is not None
 
 
 def test_null_input(table):