test/cqlpy: add from_string vector test

Motivation for this test was to show that from_string functionality
can be accesed via CQL.

test/cqlpy/test_from_string.py

@@ -0,0 +1,18 @@
+# Copyright 2024-present ScyllaDB
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+import pytest
+from .util import unique_name
+
+
+# Test that we can insert a vector from a string.
+# This is marked as scylla-only because Apache Cassandra does not support
+# such from_string syntax, but we want to have compatible string format
+# in both our from_string and to_string functions.
+# Please check abstract_type::to_string for reference.
+def test_vector_from_string(cql, test_keyspace, scylla_only):
+    table = test_keyspace + "." + unique_name()
+    cql.execute(f"CREATE TABLE {table} (pk int primary key, v vector<int, 3>)")
+    cql.execute(f"INSERT INTO {table} (pk, v) VALUES (1, '1, 2, 3')")
+    assert cql.execute(f"SELECT v FROM {table} WHERE pk=1").one().v == [1, 2, 3]