Convert "a in (b, c)" to "a == b or a == c"

[kmod]

Not super common, but can seems to help since we are particularly bad at handling a in (b, c).

       django_template.py             3.6s (2)             3.6s (2)  -0.5%
            pyxl_bench.py             3.5s (2)             3.5s (2)  -0.4%
sqlalchemy_imperative2.py             4.3s (2)             4.3s (2)  -0.9%
                  geomean                 3.8s                 3.8s  -0.6%

[tjhance]

I haven't looked too closely at your diff but the transformation in your subject line is incorrect, e.g.,

>>> n = float('nan')
>>> n in (n,n)
True
>>> n == n or n == n
False

[kmod]

oh doh that's true