Feat: Default trait for Array/Dict

[wraitii]

Fixes #3046

This does two things:

• Leverage the existing Default trait instead of adding a custom method to ArrayTrait/Felt252DictTrait
• Use that trait to create a simple new function that makes code leaner.

If the new function isn't desired, I'll remove it, but I think it's overall a good readability improvement.

NB: There is a new in BoxTrait that takes an argument. I haven't changed that.

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This change is 

[orizi]

Reviewable status: 0 of 35 files reviewed, 1 unresolved discussion (waiting on @wraitii)

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corelib/src/lib.cairo line 11 at r1 (raw file):

fn new<T, impl TDefault: Default<T>>() -> T {
    Default::default()

name is "too useful" - i have no issues with the fn itself - but i think we need a bit of a longer name at the very least.
(and the fact that Default::default() would work seems to me to make it less necessary as well)

[spapinistarkware]

Reviewed 2 of 35 files at r1, all commit messages.
Reviewable status: 2 of 35 files reviewed, 1 unresolved discussion (waiting on @orizi)

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corelib/src/lib.cairo line 11 at r1 (raw file):

Previously, orizi wrote…

name is "too useful" - i have no issues with the fn itself - but i think we need a bit of a longer name at the very least.
(and the fact that Default::default() would work seems to me to make it less necessary as well)

I don't like this function either. We can use Default::default()

[wraitii]

Reviewable status: 2 of 35 files reviewed, 1 unresolved discussion (waiting on @orizi and @spapinistarkware)

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corelib/src/lib.cairo line 11 at r1 (raw file):

Previously, spapinistarkware (Shahar Papini) wrote…

I don't like this function either. We can use Default::default()

I've removed the function.
I think a shortened form could be useful (perhaps just default()), but that would be mostly sidestepped if we had something like vec![]

[spapinistarkware]

Reviewed 5 of 21 files at r2, all commit messages.
Reviewable status: 7 of 35 files reviewed, 2 unresolved discussions (waiting on @orizi and @wraitii)

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corelib/src/debug.cairo line 24 at r2 (raw file):

fn print_felt252(message: felt252) {
    let mut arr = Default::default();

How does this actually work? With no type annotations, it can't know we want an array.

[wraitii]

Reviewable status: 7 of 35 files reviewed, 2 unresolved discussions (waiting on @orizi and @spapinistarkware)

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corelib/src/debug.cairo line 24 at r2 (raw file):

Previously, spapinistarkware (Shahar Papini) wrote…

How does this actually work? With no type annotations, it can't know we want an array.

I believe the type system deduces it from the print statement. I'm honestly not entirely sure about the type-deduction system in Cairo though.
But this compiles and runs without problem.

[orizi]

Reviewed 12 of 35 files at r1, 18 of 21 files at r2, 1 of 1 files at r3, all commit messages.
Reviewable status: 35 of 36 files reviewed, 2 unresolved discussions (waiting on @spapinistarkware and @wraitii)

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corelib/src/traits.cairo line 132 at r3 (raw file):

        @Default::default()
    }
}

Suggestion:

impl SnapshotDefault<T, impl TDefault: Default<T>, impl TDrop: Drop<T>> of Default<@T> {
    #[inline(always)]
    fn default() -> @T {
        @Default::default()
    }
}

[wraitii]

Reviewable status: 35 of 36 files reviewed, 2 unresolved discussions (waiting on @orizi and @spapinistarkware)

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corelib/src/traits.cairo line 132 at r3 (raw file):

        @Default::default()
    }
}

Done

[orizi]

Reviewed 1 of 35 files at r1, 8 of 8 files at r4, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @spapinistarkware)

[spapinistarkware]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @wraitii)

[spapinistarkware]

Looks like there are conflicts. If you resolve them, I'll merge

[orizi]

Reviewed 16 of 16 files at r5, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @wraitii)

[orizi]

Reviewed 5 of 5 files at r6, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @wraitii)

[lambda-0x]

wouldn't it be better to have both ArrayTrait::new() and Default::default() because when default is used and type is not annotated manually it, reader would need to infer the type by looking at the variable usage.

And I like being more explicit way more. similar to rust where there is default but people still prefer to use new methods defined on type over default.

Not to mention this would be a breaking change for anyone using new methods.