Deflake acceptance tests

[lennartkats-db]

Changes

This PR makes some tactical changes to the acceptance test configuration to deflake them. They've been quite flaky for me, especially in agent settings. I asked an agent to stress test them and address problems:

• The default timeout for tests is now 30s instead of 20s (common cause of failures)
• run-local-node tests now automatically use a free port (very common cause of failures)
• The timeout self-test is less timing sensitive (rare cause of failures)

Tests

• Stress tested by AI

[eng-dev-ecosystem-bot]

Run: 18095531078

	Env	✅​pass	🙈​skip
✅​	aws linux	312	531
✅​	aws windows	313	530
✅​	aws-ucws linux	425	428
✅​	aws-ucws windows	426	427
✅​	azure linux	312	530
✅​	azure windows	313	529
✅​	azure-ucws linux	425	427
✅​	azure-ucws windows	426	426
✅​	gcp linux	311	532
✅​	gcp windows	312	531