test(flagd): drop the per-scenario /stop in e2e teardown once the testbed includes flagd-testbed#396 #1891

Problem

ProviderSteps.tearDown (providers/flagd/src/test/java/.../e2e/steps/ProviderSteps.java) POSTs /stop to the launchpad after every scenario. That makes every /start a cold flagd start.

open-feature/flagd-testbed#396 makes /start reuse the running flagd and restore the baseline flag state in place. Isolation no longer needs the /stop, and keeping it means the suite never gets the speedup.

Proposal

After bumping the testbed to a release that includes open-feature/flagd-testbed#396, remove the /stop block from tearDown. Keep ContainerPool.release and the NoOp provider swap.

Evidence

Tested locally with the /stop removed, against an image built from flagd-testbed#396 and one built from testbed main. All 590 tests (in-process 224, RPC 214, file 152) passed in every run. Wall time (in-process / RPC / file):

The machine was shared with other test runs, so treat the times as indicative. Without flagd-testbed#396, dropping /stop gains nothing, which is why this should wait for the bump.