Fixes #407

TestPlatformActivity_StreamingLogs in internal/pkg/platform/activity_test.go was flaky because cancellation was driven by time.Sleep goroutines, making call count assertions race against wall-clock timing on slow CI runners. Replaces the sleep-based cancellation with call-count-driven cancellation using sync/atomic.Int32 counters inside the mock's Run callback, so cancel() is called only after the expected number of Activity invocations. Verified by the deterministic call counts now asserted via cm.API.AssertNumberOfCalls.