feat(corelib): Result iterator

[cairolover]

Adds IntoIter and Iter implementations for Result<T, E>.
Follows a format similar to SpanIter and ArrayIter, with a new ResultIter struct.

[reviewable-StarkWare]

This change is 

[cairolover]

Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion

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corelib/src/test/result_test.cairo line 2 at r2 (raw file):

use crate::result::{Result, ResultTraitImpl};
use crate::iter::{IntoIterator, Iterator};

should this not be included automatically in the prelude?

[orizi]

Reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 3 unresolved discussions (waiting on @cairolover)

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corelib/src/result.cairo line 577 at r2 (raw file):

impl ResultIntoIterator<T, E, +Copy<T>, +Destruct<T>, +Destruct<E>> of IntoIterator<Result<T, E>> {
    type IntoIter = ResultIter<T>;

consider just using OptionIter here after it is merged.

Suggestion:

impl ResultIntoIterator<T, E, +Copy<T>, +Destruct<T>, +Destruct<E>> of IntoIterator<Result<T, E>> {
    type IntoIter = OptionIter<T>;

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corelib/src/test/result_test.cairo line 265 at r2 (raw file):

    let x: Result<u32, ByteArray> = Result::Ok(5);
    let mut x_iter = x.into_iter();
    assert!(x_iter.next() == Option::Some(5));

Suggestion:

    assert!(x_iter.next() == Option::Some(5));
    assert!(x_iter.next() == Option::None);