Make list_cy more idiomatic

[boothby]

This is a more idiomatic implementation of cy_list, which avoids several performance pitfalls. On my machine, this results in about a 2x improvement in performance. This PR is incompatible with #2; maybe they should be separate tests.

[00sapo]

I had already tried to use cdef list internal_list and list in the signature of make_list, but slowed down the code for me... That's the point: Cython is completely unpredictable

[bconstanzo]

Chiming in here, I tried basically the same optimization/cleanup that @boothby did, on my machine I got almost an order of magnitude speedup:

In [9]: %timeit list_cy.iterate_list(a_list)
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
385 ms ± 6.15 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

In [10]: %timeit list_cyo.iterate_list(a_list)
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
1000000.0007792843
2.71 s ± 182 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

Where list_cy is the optimized module and list_cyo is the code as you have right now in the repo. Give this a double check, it certainly improves times for cython.

[mcabbott]

FWIW, the equivalent change to the Julia version would also be more idiomatic, and much quicker:

make_list() = [fill(0.1, 10^4) for _ in 1:10^4];

Similar changes could also be made to iterate_list, but almost all the time is spent in make_list.

[boothby]

I noticed that the majority of the time was spent in make_list when I did the implementation for #2, too. @00sapo it might be interesting to time the make_list and iterate_list calls separately.

[tuffnatty]

i is unused here?

[tuffnatty]

i, j are also unused here