avoid high load of loop function because of no sleep in while()

[tongtybj]

We found two problems when using this package:

• An infinite and nonstop loop process in initialize(), if there is no Motive server in the same network. This will lead to a very high load for CPU (occupy entire one core of CPU).Then, we add following line to relieve the load: https://github.com/tongtybj/mocap_optitrack/blob/befbeaf2e2180db6cf0571a57e1510c21fd4b9bf/src/mocap_node.cpp#L96

• A nonstop loop process in run(), when updateDataModelFromServer() returns false. This always happens when new packet is not sent from Motive. This also leads to a very high load for CPU Then, we add following line to relive the load: https://github.com/tongtybj/mocap_optitrack/blob/befbeaf2e2180db6cf0571a57e1510c21fd4b9bf/src/mocap_node.cpp#L145-L146

We are using this package for Drone in both indoor and outdoor environments, and the high load of mocap_node significantly limits the computation resource to perform other process such as image processing. So, we think this PR is very critical for users who use onboard compact computes.

[tonybaltovski]

@tongtybj Can you fix that minor linting error causing the CI to fail, please?

[tongtybj]

@tonybaltovski

Sorry for the linting error. I have fixed it.

[tonybaltovski]

Thanks @tongtybj !!