Remove duplicate poly definitions and parallelize evaluation

[Cesar199999]

Closes #9. Removes duplicated EqPolynomial and MultilinearPolynomial definitions by removing the
polynomial.rs file. Both types are now only in the eq.rs. No other changes were required in
the codebase as the types in polynomial.rs were not used anywhere else.

In addition, this PR parallelizes the EqPolynomial::evaluate function using Rayon's into_par_iter
method, and adds benchmarks for the function. The benchmarks (on my HP EliteBook 840 G7) show that
the parallelized version of the function performs better for large instances:

evaluate_incremental/2^1
                       time:   [13.666 µs 13.717 µs 13.768 µs]
                       change: [+6812.6% +6937.9% +7055.6%] (p = 0.00 < 0.05)
                       Performance has regressed.
Found 6 outliers among 100 measurements (6.00%)
 3 (3.00%) low mild
 2 (2.00%) high mild
 1 (1.00%) high severe
evaluate_incremental/2^3
                       time:   [14.974 µs 15.108 µs 15.262 µs]
                       change: [+1966.1% +2019.2% +2074.8%] (p = 0.00 < 0.05)
                       Performance has regressed.
Found 11 outliers among 100 measurements (11.00%)
 4 (4.00%) high mild
 7 (7.00%) high severe
evaluate_incremental/2^5
                       time:   [18.359 µs 18.562 µs 18.785 µs]
                       change: [+545.64% +552.71% +559.60%] (p = 0.00 < 0.05)
                       Performance has regressed.
Found 3 outliers among 100 measurements (3.00%)
 3 (3.00%) high mild
evaluate_incremental/2^7
                       time:   [28.191 µs 28.402 µs 28.628 µs]
                       change: [+145.80% +148.43% +151.12%] (p = 0.00 < 0.05)
                       Performance has regressed.
Found 4 outliers among 100 measurements (4.00%)
 3 (3.00%) high mild
 1 (1.00%) high severe
evaluate_incremental/2^9
                       time:   [55.980 µs 57.917 µs 60.159 µs]
                       change: [+21.740% +23.970% +26.544%] (p = 0.00 < 0.05)
                       Performance has regressed.
Found 8 outliers among 100 measurements (8.00%)
 4 (4.00%) high mild
 4 (4.00%) high severe
evaluate_incremental/2^11
                       time:   [112.90 µs 114.63 µs 116.48 µs]
                       change: [-38.754% -37.528% -35.992%] (p = 0.00 < 0.05)
                       Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
 2 (2.00%) high mild
evaluate_incremental/2^13
                       time:   [277.95 µs 282.42 µs 287.06 µs]
                       change: [-62.248% -61.689% -61.053%] (p = 0.00 < 0.05)
                       Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
 1 (1.00%) high mild
 1 (1.00%) high severe
evaluate_incremental/2^15
                       time:   [953.95 µs 986.72 µs 1.0333 ms]
                       change: [-69.195% -68.426% -67.543%] (p = 0.00 < 0.05)
                       Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
 2 (2.00%) high mild
 1 (1.00%) high severe
evaluate_incremental/2^17
                       time:   [3.4105 ms 3.4747 ms 3.5640 ms]
                       change: [-71.229% -70.680% -69.911%] (p = 0.00 < 0.05)
                       Performance has improved.
Found 5 outliers among 100 measurements (5.00%)
 2 (2.00%) high mild
 3 (3.00%) high severe
evaluate_incremental/2^19
                       time:   [11.854 ms 12.042 ms 12.241 ms]
                       change: [-75.035% -74.632% -74.186%] (p = 0.00 < 0.05)
                       Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
 1 (1.00%) high mild

[srinathsetty]

Thanks for the PR! This improvement might apply here as well: https://github.com/microsoft/Nova/blob/4f8f3e782b172e98d6d741b29e5bc671ab5b93a6/src/spartan/polys/eq.rs#L36

[Cesar199999]

Thanks for the PR! This improvement might apply here as well: https://github.com/microsoft/Nova/blob/4f8f3e782b172e98d6d741b29e5bc671ab5b93a6/src/spartan/polys/eq.rs#L36

Thank you. Sure, I'll create a PR there too.

[Cesar199999]

Hey @srinathsetty, is it possible to merge this?