fix: update rev_iter2 to yield indices in descending order

[Asterless]

Based on #2850. This pull request updates the rev_iter2 for the Deque data structure to ensure that the index values correctly reflect their position when iterating in reverse order. The index now starts from length - 1 and decrements with each step, rather than starting from 0 and incrementing. This change makes the reverse iterator's behavior more intuitive and consistent with typical expectations.

[peter-jerry-ye-code-review]

Test logic error in rev_eachi test case

Category
Correctness
Code Snippet
Line 189: if index != j - 2 || elem != i - 1 {
failed = true
}
Recommendation
Change the condition to if index != j || elem != i - 1 since j now correctly tracks the expected index
Reasoning
The test is using j - 2 which appears to be an incorrect adjustment. Since j now starts at 6 and decrements to match the new indexing behavior, the comparison should be direct index != j

Inconsistent variable naming in iterator implementation

Category
Maintainability
Code Snippet
Lines 1613-1627: let mut j = len - 1
...
j -= 1
Recommendation
Rename variable j to index or current_index to better reflect its purpose as the index counter
Reasoning
The variable name j is not descriptive and makes the code harder to understand. Since this variable represents the current index being yielded, a more descriptive name would improve code readability

Test initialization values need verification

Category
Correctness
Code Snippet
Lines 185-186: let mut i = 6
let mut j = 6
Recommendation
Verify that initial values are correct: for a deque of length 5, j should start at 4 (length-1), not 6
Reasoning
The test uses a deque of 5 elements [1,2,3,4,5], so the initial index should be 4 (length-1), but j is initialized to 6. This suggests either the test data or initialization values are incorrect

[coveralls]

Pull Request Test Coverage Report for Build 1626

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.853%

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Totals
Change from base Build 1621:	0.0%
Covered Lines:	9785
Relevant Lines:	10890

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💛 - Coveralls

[peter-jerry-ye]

We need to discuss this furthur before making changes.