Fix clippy lints

[linkmauve]

This Pull Request fixes/closes no issue.

It changes the following:

• Remove an unneeded .to_string().
• Replace a bunch of manual impl Defaults with #[derive(Default)]
• Make explicit the failure mode of a Duration subtraction.

[jedel1043]

This was already fixed by #4513

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	50,595	50,595	0
Passed	47,678	47,678	0
Ignored	2,036	2,036	0
Failed	881	881	0
Panics	0	0	0
Conformance	94.23%	94.23%	0.00%

[linkmauve]

I’ve rebased on top of main, there are still changes worth it in this PR, since I’m running clippy nightly locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.00%. Comparing base (6ddc2b4) to head (6048564).
⚠️ Report is 579 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4517      +/-   ##
==========================================
+ Coverage   47.24%   57.00%   +9.76%     
==========================================
  Files         476      503      +27     
  Lines       46892    57410   +10518     
==========================================
+ Hits        22154    32727   +10573     
+ Misses      24738    24683      -55     

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