Implement round-ties-to-even for Duration Debug for consistency with f64

[josh-kaplan]

Summary

This PR proposes a fix for #103747 implementing IEEE-754 S4.3 roundTiesToEven for Duration Debug implementation.

Testing

Added new test in time.rs for validating roundTiesToEven behavior in Duration formatting. Reran all debug formatting tests in time.rs with ./x test library/coretests --test-args time::debug_formatting.

[rustbot]

r? @scottmcm

rustbot has assigned @scottmcm.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[hkBst]

Maybe also add a test-case for println!("{:.0?}", Duration::MAX);, unless it is already there?

[josh-kaplan]

Maybe also add a test-case for println!("{:.0?}", Duration::MAX);, unless it is already there?

Fair! It looks like it already exists on line 330 in debug_formatting_extreme_values.

I also updated the comment above the new rounding behavior to accurately reflect the behavior change.