val in self.channels.items() can be float

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Hi fellow,

thanks a looot for your library. Real nice work.

I ran into an issue (can't tell you the origin), but by using a constant stream following line in _Controller.py might create a float, which later on will crash the program:
```
# Get all channels values
for key, val in self.channels.items():
# If channel in frame
if key - first < len(self.__frame):
self.__frame[key - first] = int(val[0])`
```

i placed an int() around the val[0]. Not sure if that's in general a good idea.

but it fixed the issue, that otherwise at this call would break the runtime.

````
def _transmit(self, frame: List[int], first: int):
# Convert to a bytearray and pad the start of the frame
# We're transmitting direct DMX data here, so a frame must start at channel 1, but can end early
try:
data = bytearray(([0] * (first - 1)) + frame)
# The first byte in the type, and is `0` for normal DMX data
data.insert(0, 0)

# Write
self.__device.send_break(100e-6)
sleep(10e-6)
self.__device.write(data)
except:
print("bad request")`
```

as you see I made a try / except for myself.

Start in _Controller.py at the channel-value loop and inspect how values from self.channels.items() reach _transmit. Reproduce the constant-stream case that produces a float, then verify the chosen handling preserves valid DMX frame data and prevents the bytearray conversion from failing.

Written by the indexing model from the issue text.