Added *_eq const folding.

[orizi]

Stack:

• Added const-folding *_eq with 0 into *_iz_zero. #6454
• Const propagation for ops with special operands. #6453
• Refactored setting constant and returning statement together. #6436
• Added *_eq const folding. #6435 ⬅

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.

---

This change is 

[gilbens-starkware]

Reviewed all commit messages.
Reviewable status: 0 of 2 files reviewed, 1 unresolved discussion (waiting on @orizi)

---

crates/cairo-lang-lowering/src/optimizations/const_folding.rs line 527 at r2 (raw file):

    /// The set of functions that check if a number is zero.
    nz_fns: OrderedHashSet<ExternFunctionId>,
    /// The set of functions that check if a numbers are equal.

Suggestion:

 /// The set of functions that check if numbers are equal.

[gilbens-starkware]

Reviewed 1 of 2 files at r1, 1 of 1 files at r3.
Reviewable status: all files reviewed (commit messages unreviewed), all discussions resolved (waiting on @orizi)

[gilbens-starkware]

Reviewed all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @orizi)