Fail all pending requests during a reset

[puddly]

If the serial link is slow enough (i.e. a TCP coordinator), it appears that a race condition can arise where a watchdog poll can coincide with an intentional reset request. During a reset, all pending requests should be cancelled.

CC @tube0013

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (fc4a131) 98.07% compared to head (ea87e1c) 98.01%.
Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #229      +/-   ##
==========================================
- Coverage   98.07%   98.01%   -0.07%     
==========================================
  Files          43       43              
  Lines        3695     3719      +24     
==========================================
+ Hits         3624     3645      +21     
- Misses         71       74       +3     

Files	Coverage Δ
zigpy_znp/api.py	96.63% <100.00%> (+0.07%)	⬆️
zigpy_znp/exceptions.py	100.00% <100.00%> (ø)
zigpy_znp/zigbee/application.py	94.96% <66.66%> (-0.23%)	⬇️
zigpy_znp/utils.py	97.82% <80.00%> (-2.18%)	⬇️

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