hasattr() performance is bad on a slot that has no value

Bug report

Bug description:

Compare these two timeit invocations:

$ python3.14 -m timeit -s 'class Test: pass' -s 't = Test()' 'hasattr(t,"x")'
10000000 loops, best of 5: 33.5 nsec per loop
$ python3.14 -m timeit -s 'class Test: __slots__ = ("x",)' -s 't = Test()' 'hasattr(t,"x")'
1000000 loops, best of 5: 241 nsec per loop

Observe that in the case where Test.x is a slot, hasattr takes 241 ns to return False while it only takes 33.5 ns when there is no Test.x slot.

Peter Bierma advised me to file an issue when I asked about this in Discourse.

CPython versions tested on:

3.14, 3.13, 3.12

Operating systems tested on:

Linux

首先重現 issue 中的兩個 Python 3.14 timeit 命令，並比較缺少屬性的情況與未賦值 slot 的情況。追蹤造成差異的 slot 查找與 hasattr 路徑。完成的標準是未賦值 slot 的情況得到可測量的改善，同時不改變 hasattr 的 False 結果或現有行為。