This commit addresses multiple issues in the DockerStatsEngine:Race Condition Fixes:- Add context cancellation checks in taskContainerMetricsUnsafe to prevent  metrics collection on containers that are in the middle of being  cleaned up.- Implement removeContainerFromAllTasksUnsafe method to handle orphaned  container cleanup. This prevents container leaks when the Docker Task Engine  has already cleaned up the container but the stats engine still has it tracked.This fixes the condition where the ECS agent starts logging messageslike this continuously for a particular container:```ecs_agent_logs/ecs-agent.log:1496:level=error time=2025-09-12T11:18:54Z msg="Error collecting cloudwatch metrics for container" container="111222333444555" error="need at least 1 non-NaN data points in queue to calculate CW stats set"ecs_agent_logs/ecs-agent.log:1500:level=error time=2025-09-12T11:19:14Z msg="Error collecting cloudwatch metrics for container" container="111222333444555" error="need at least 1 non-NaN data points in queue to calculate CW stats set"ecs_agent_logs/ecs-agent.log:1507:level=error time=2025-09-12T11:19:34Z msg="Error collecting cloudwatch metrics for container" container="111222333444555" error="need at least 1 non-NaN data points in queue to calculate CW stats set"```Unrelated but also rename engine_linux.go to engine_unix.go so that thispackage can compile on macOS more easily.