types_test: test cases for big varints

Added test cases for varints that can't be contained in any primitive.

Author: muzarski

scylla/src/transport/cql_types_test.rs

@@ -116,6 +116,9 @@ fn varint_test_cases() -> Vec<&'static str> {
         "-129",
         "123456789012345678901234567890",
         "-123456789012345678901234567890",
+        // Test cases for numbers that can't be contained in u/i128.
+        "1234567890123456789012345678901234567890",
+        "-1234567890123456789012345678901234567890",
     ]
 }