feat(corelib): range is_empty

[julio4]

Add core::ops::RangeTrait with:

fn is_empty(self: @Range<T>) -> bool

Returns true if the range contains no items.

Examples

assert!(!(3_u8..5_u8).is_empty());
assert!( (3_u8..3_u8).is_empty());
assert!( (3_u8..2_u8).is_empty());

[reviewable-StarkWare]

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[orizi]

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[orizi]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @julio4)

[gilbens-starkware]

Reviewed 2 of 4 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @julio4)

[orizi]

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Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @julio4)