test: prove package initialization semantics

test/wcc/data/r778_stream_write_flush/case.ww

@@ -10,7 +10,7 @@ export fn main() i32 = {
     let msrc: io.stream = &mst.vt;
     let rbuf: [8]u8;
     let wbuf: [8]u8;
-    let b: bufio.stream = bufio.init(msrc, rbuf[0:8], wbuf[0:8]);
+    let b: bufio.stream = bufio.newstream(msrc, rbuf[0:8], wbuf[0:8]);
     let vs: io.stream = &b.vt;
     let payload: [5]u8;
     payload[0] = 104u8; payload[1] = 105u8;