Need to ensure ExecutionContext is destroyed before parent CudaEngine.

[theHamsta]

E.g.

ok

pub(crate) struct TrtxGraph<'context> {
    exec: ExecutionContext<'context>,
    _engine: CudaEngine<'context>,
    cuda_stream: Arc<CudaStream>,
}

not ok

pub(crate) struct TrtxGraph<'context> {
    _engine: CudaEngine<'context>,
    exec: ExecutionContext<'context>,
    cuda_stream: Arc<CudaStream>,
}

[theHamsta]

In above sample, we guarantee on the Rust level that whenever you execute methods on any of the objects, both are valid. However, trt also checks direct destructor order