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

[ruiyangke]

Fix incorrect type check in buffered_iternext() that prevented the fast path from ever being taken, slowing down iteration over buffered binary files.

Since tp is already a type object, Py_IS_TYPE(tp, X) expands to Py_TYPE(tp) == X, which compares the type itself against BufferedReader. This is always false, so the fast path was never taken.

pyperf benchmark:

+----------------+---------+-----------------------+
| Benchmark      | buggy   | fixed                 |
+================+=========+=======================+
| iteration      | 3.05 ms | 2.04 ms: 1.49x faster |
+----------------+---------+-----------------------+

Closes: #144380

• Issue: Fast path in buffered_iternext is never taken due to incorrect type check #144380

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[colesbury]

Thanks for catching this. Would you please add a news entry (blurb)?

[ruiyangke]

Thanks for catching this. Would you please add a news entry (blurb)?

Thanks, new entry added

[miss-islington-app]

Thanks @ruiyangke for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-144389 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-144390 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86-64 macOS 3.13 (tier-2) has failed when building commit 51fccc6.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1483/builds/1215) and take a look at the build logs.
4. Check if the failure is related to this commit (51fccc6) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1483/builds/1215

Failed tests:

• test.test_multiprocessing_spawn.test_processes

Failed subtests:

• test_repr_rlock - test.test_multiprocessing_spawn.test_processes.WithProcessesTestLock.test_repr_rlock

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.13.billenstein-macos/build/Lib/test/_test_multiprocessing.py", line 1493, in test_repr_rlock
    self.assertEqual('<RLock(SomeOtherThread, nonzero)>', repr(lock))
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: '<RLock(SomeOtherThread, nonzero)>' != '<RLock(None, 0)>'
- <RLock(SomeOtherThread, nonzero)>
+ <RLock(None, 0)>