gh-144380: Fix incorrect type check in buffered_iternext()

The condition used Py_IS_TYPE(tp, ...) where tp is already a `type`,
this made the fast path unreachable.
Avoid unnecessary method resolution checks in the iteration hot path,
resulting in ~49% faster line iteration for `io.BufferedReader`.

Author: ruiyangke

Misc/NEWS.d/next/Library/2026-02-01-15-25-00.gh-issue-144380.U7py_s.rst

@@ -0,0 +1 @@
+Improve performance of :class:`io.BufferedReader` line iteration by ~49%.

Modules/_io/bufferedio.c

@@ -1505,8 +1505,8 @@ buffered_iternext(PyObject *op)
 
     _PyIO_State *state = find_io_state_by_def(Py_TYPE(self));
     tp = Py_TYPE(self);
-    if (Py_IS_TYPE(tp, state->PyBufferedReader_Type) ||
-        Py_IS_TYPE(tp, state->PyBufferedRandom_Type))
+    if (tp == state->PyBufferedReader_Type ||
+        tp == state->PyBufferedRandom_Type)
     {
         /* Skip method call overhead for speed */
         line = _buffered_readline(self, -1);