Set default parameter for get_channels_for_device

Optional device specifier: Adjusted get_channels_for_device function to
include a default empty string parameter. Enables calls without
specifying a device, reducing the need for client code to handle default
cases explicitly.

src/limedriver/limedriver.pyx

@@ -723,6 +723,6 @@ def get_device_list():
     cdef vector[string] devices = getDeviceList()
     return [device.decode('utf-8') for device in devices] 
 
-def get_channels_for_device(device):
+def get_channels_for_device(device = ""):
     cdef pair[int, int] channels = getChannelsFromInfo(device)
     return channels.first, channels.second