Add bail-on-test-failure handling to Testem

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What this task asks for

Add configurable early bailout on test failures across runners, reporters, and exit codes. Add `bail_on_test_failure` with false, true, or positive-integer thresholds and validate invalid values. Stop on the configured non-skipped failure count and expose resettable reason, launcher, count, and failed-test state. Emit bailout summaries through TAP, Dot, TeamCity, and XUnit reporters. Make runner, server, and application abort operations idempotent and suppress later results or errors. Guard Mocha, Jasmine2, and QUnit browser emissions after abort, including deferred callbacks. Return a distinct bail exit error using only the reported bail reason and pre-bail test count.