SchunkGripperProcess.move()/open()/close() silently do nothing until speed is set

### Description

When using `SchunkGripperProcess`, calling `move()`, `open()`, or `close()` right after construction does not move the gripper. The connection succeeds and no error is raised — the fingers just don't move.

### Cause

`move()` issues a `MOVE_POS` command but never sets a target velocity. The gripper's default `set_vel` is `0`, so the motion completes "instantly" with zero speed and the fingers don't move. The fingers only move once `gripper.speed = ` has been set beforehand (as the `__main__` example in `schunk_process.py` does).

### Reproduce

```python
g = SchunkGripperProcess(usb_interface=PORT)
g.open().wait() # nothing happens
g.close().wait() # nothing happens
```

Adding `g.speed = 0.04` before the moves fixes it.

### Suggested fix

Either initialise a sensible default velocity in `__init__` / `_gripper_process_main`, have `move()` set a default speed when none has been configured, or at minimum document that `speed` must be set before the first move.