#1187 perf(runner): dispatch files longest first by the previous run's timings

What and why

• With workers > 1, the runner orders file units by their duration in the previous report.json, longest first (packages/e2e/src/run/units.ts longestFirst). Files new since that run go first; ties keep collection order.
• Before, a long file collected late could start last and hold the run open after every other worker went idle.
• Report order is unchanged; it is sorted separately. Serial runs are untouched.

Verified

Ran it locally: yes

• apps/web-benchmark, e2e run --workers 7, second run so a report exists. The suite is bounded by virtualized-table (~70s), which now starts first.

	main	this branch
run 1	77.9s	77.3s (no previous report)
run 2	78.7s	72.2s