Implement 'Sum' and 'Product' on field types

[andrewmilson]

This change is 

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 95.26%. Comparing base (e9aa5fc) to head (5960d2d).

Files	Patch %	Lines
src/core/fields/mod.rs	0.00%	26 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #497      +/-   ##
==========================================
- Coverage   95.57%   95.26%   -0.32%     
==========================================
  Files          58       58              
  Lines        8884     8913      +29     
  Branches     8884     8913      +29     
==========================================
  Hits         8491     8491              
- Misses        344      373      +29     
  Partials       49       49              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alonh5]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @andrewmilson and @ohad-starkware)

a discussion (no related file):
Could you give some context as to why we need these and where they're going to be used?

---

[andrewmilson]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @alonh5 and @ohad-starkware)

a discussion (no related file):

Previously, alonh5 (Alon Haramati) wrote…

Could you give some context as to why we need these and where they're going to be used?

Computing the sum and product is a common operation. I do it in my next PRs. Also there is an open PR that could already use this https://github.com/starkware-libs/stwo/pull/506/files#diff-bf237a27a0c3209b3f17119d6b863f0b16a65d0e7950f07dcca80ccbdf14a147R114

---

[ohad-starkware]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @alonh5)

---

src/core/fields/mod.rs line 169 at r1 (raw file):

    ($field_name: ty, $field_size: ident) => {
        use std::iter::{Product, Sum};

is the space here by intent?