Cython Fibonacci Sequence
Using one less variable seems faster:
cdef int fib_c(int n):
    if n == 0:
        return 0
    cdef int a = 0
    cdef int b = 1
    for _ in range(n - 1):
        a, b = b, a + b
    return b

Running your test on my machine:
Original = 2.934 s
Improved = 1.522 s