gh-119109: functools.partial.fallforward fix

[dg-pb]

#119109

I went with option 1. It is cleaner, faster and has a natural flow.

Before:

from functools import partial

def func(a, b, c=0):
    return a - b - c

p1 = partial(func, 1)

print(p1(2))    # -1
%timeit p1(2)   # 100 ns

p1.keywords['c'] = 1
print(p1(2))    # -2
%timeit p1(2)   # 234 ns

del p1.keywords['c']
print(p1(2))    # -1
%timeit p1(2)   # 144 ns

After:

p1 = partial(func, 1)

print(p1(2))    # -1
%timeit p1(2)   # 100 ns

p1.keywords['c'] = 1
print(p1(2))    # -2
%timeit p1(2)   # 234 ns

del p1.keywords['c']
print(p1(2))    # -1
%timeit p1(2)   # 100 ns

• Issue: functools.partial does not re-set vector call. #119109