feat(deque): add @deque.iter2() and @deque.copy()

[rami3l]

Disclaimer: The coverage improving part of this PR was generated by an LLM agent as part of an experiment.

Summary

New methods added:

• deque/deque.mbt: Implemented the copy method, which creates a new copy of the deque.
• deque/deque.mbt: Added the iter2 method, which iterates over the deque with index and element pairs.
• deque/deque.mbti: Updated the impl T block to include the copy and iter2 methods.

Optimizations:

• deque/deque.mbt: Applied iter2's implementation method to the existing iter.

Coverage

coverage of `deque/deque.mbt`: 87.4% -> 93.7%

[coveralls]

Pull Request Test Coverage Report for Build 4296

Details

• 14 of 19 (73.68%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 81.254%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
deque/deque.mbt	14	19	73.68%

Totals
Change from base Build 4295:	0.06%
Covered Lines:	4625
Relevant Lines:	5692

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💛 - Coveralls