fix: Increase iframe unload timeout

[FrederikBolding]

Increase the iframe unload timeout significantly to prevent issues where the timeout would be too low and thus the workaround wouldn't be effective.

When testing this I've seen spikes up to 200ms, but mostly in the 10-50ms range. Though, we've decided to bump to a full second, since we don't expect to hit this often (if at all).

https://consensyssoftware.atlassian.net/browse/WPC-987

---

Note

Low Risk
Low risk: a single timeout constant is increased to reduce flaky iframe teardown; the main behavioral change is waiting longer before removing the iframe in edge cases.

Overview
Increases the withTimeout duration used during IframeExecutionService.terminateJob teardown (waiting for the about:blank load) from 10ms to 1_000ms before removing the iframe, making unload/cleanup more reliable under slower load events.

^{Reviewed by Cursor Bugbot for commit 747ccab. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.56%. Comparing base (353d009) to head (747ccab).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3971   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files         429      429           
  Lines       12363    12363           
  Branches     1942     1942           
=======================================
  Hits        12185    12185           
  Misses        178      178           

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