Ensure version-specific unit tests cover command sending format

[puddly]

In the future, we need to migrate bellows to a more robust framework that tests end-to-end command serialization and response parsing. Until then, I've replaced all blind mocks with those that also try to serialize the command.

There was a single error with EZSPv8 that has since been corrected.

Fixes #640

[puddly]

I've migrated test_application.py as well.

A future PR will add end-to-end testing of the entire command serialization format and adapter response for every EZSP version, hopefully like we do in zigpy-znp.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.10%. Comparing base (61f7ec0) to head (55370ed).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #639      +/-   ##
==========================================
- Coverage   99.16%   99.10%   -0.06%     
==========================================
  Files          50       50              
  Lines        3460     3462       +2     
==========================================
  Hits         3431     3431              
- Misses         29       31       +2     

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