Small cleanups to the protocol handler

[bdraco]

needs #463 first

• Add some typing
• Avoid some bytes concat

[codecov]

Codecov Report

Merging #465 (a243126) into dev (07df76b) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #465      +/-   ##
==========================================
+ Coverage   92.48%   92.50%   +0.01%     
==========================================
  Files          20       20              
  Lines        2223     2227       +4     
  Branches      274      274              
==========================================
+ Hits         2056     2060       +4     
  Misses        123      123              
  Partials       44       44              

Files	Coverage Δ
pyhap/hap_event.py	100.00% <100.00%> (ø)
pyhap/hap_handler.py	86.64% <100.00%> (ø)
pyhap/hap_protocol.py	99.39% <100.00%> (+0.01%)	⬆️