test: prove package initialization semantics

test/wcc/data/r778_stream_read_unread/case.ww

@@ -12,7 +12,7 @@ export fn main() i32 = {
     let msrc: io.stream = &mst.vt;
     let rbuf: [8]u8;
     let wbuf: [4]u8;
-    let b: bufio.stream = bufio.init(msrc, rbuf[0:8], wbuf[0:4]);
+    let b: bufio.stream = bufio.newstream(msrc, rbuf[0:8], wbuf[0:4]);
     let vs: io.stream = &b.vt;
     let out: [4]u8;
     let rd1 = io.read(vs, out[0:3]);