added disconnect listener

[FieryRMS]

fixes #38
self.__video_socket.recv returns an empty byte string when device gets disconnected.
I also added a new event EVENT_DISCONNECT that is called when disconnect happens.

py-scrcpy-client/scrcpy/core.py

Line 227 in f94749b

raw_h264 = self.__video_socket.recv(0x10000)

[codecov-commenter]

Codecov Report

Merging #40 (ca55a2b) into main (f94749b) will decrease coverage by 0.17%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
- Coverage   98.34%   98.17%   -0.18%     
==========================================
  Files           3        3              
  Lines         543      547       +4     
==========================================
+ Hits          534      537       +3     
- Misses          9       10       +1     

Flag	Coverage Δ
unittests	98.17% <85.71%> (-0.18%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
scrcpy/core.py	93.23% <83.33%> (-0.62%)	⬇️
scrcpy/const.py	100.00% <100.00%> (ø)

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