Ensure panda joint limits have the proper type

[AndyZe]

No description provided.

[rhaschke]

I believe that our code should be robust against being fed with integers. Other users might face the same issue.
@AndyZe, where exactly did you face a problem?

[AndyZe]

I'm not sure joint_limits.yaml types were causing an issue anywhere, but maybe it will fix the issue discussed here. (moveit2 423)

In moveit2_servo, there were some warnings like this coming from a different yaml file:

InvalidParameterTypeException(moveit_servo.collision_check_rate): parameter 'moveit_servo.collision_check_rate' has invalid type: expected [double] got [integer]

I made a PR to fix the Servo types here. I guess it likely would not have caused any runtime errors but good to fix anyway.

The code where these parameters get parsed (in moveit2_servo) is here. I'll try to test if the error handling there is working correctly.

[AndyZe]

Going to merge now so we can see if the flaky Servo tests are fixed.