[jochen-testingbot]

Item 1 of the follow-up list. This branch is built on #63 (--timeout), so merge #63 first. After that, this PR's diff is just the one fail-fast commit.

What

--fail-fast for maestro, espresso and xcuitest:

• A failure counts once it won't be retried:
  • Maestro: a flow whose latest attempt failed after using up the --retry budget, or a run that ended without passing and without any flows.
  • Espresso/XCUITest: a failed run in the last --retry round. Their retries run in rounds after all runs finish, so fail-fast only acts in the last round.
• When that happens, the CLI cancels the runs still queued or running, using the same stopActiveRuns as Ctrl-C and --timeout.
• It then keeps polling until those runs have stopped, and reports as usual: summary, --report, --download-artifacts, JSON and the CI job summary. The result is failed with error: "Stopped after the first failure (--fail-fast)", exit code 2.
• After the cancel, no new retries start (Maestro would otherwise retry the cancelled flows). Completion is then decided by the run states alone.
• --fail-fast with --async is rejected.

Tests

• tsc, eslint and prettier pass.
• jest: 868 passed.
• New tests:
  • The other runs are cancelled and their stop is waited for.
  • A flow still within its retry budget does not trigger fail-fast; the retry failing does.
  • Cancelled flows are not retried.
  • Espresso stops only the busy runs, and waits for the last retry round.
  • The --async combination is rejected.