test: pass the bounded attempt deadline to child requests #4024

Follow-up from #4017 (#3861).

Problem. An open inside a test attempt gets no request deadline when the test itself is unbounded. That holds even when the scheduler enforces a timeout on that attempt. As a result, the launch-confirmation re-press added in #4017 never runs inside test. This is not a regression from main.

Required behavior.

• Expose each attempt's actual deadline to its child requests: the scheduler's attempt timeout, capped by any parent deadline.
• With that in place, open --launch-url inside a bounded test attempt can re-answer the "Open in" prompt.
• Attempts that are truly unbounded stay without a deadline.