decouple error count channels from channels in 1553 channel handles

[dbendele]

Is your feature request related to a problem? Please describe.
decouple the error count channels from the 1553 channels since the error count channels are created when the custom device initializes and, in the current implementation, are not at all dependent on the number of hardware channels in the configuration.

Describe the solution you'd like
Decouple error count channels from HW channels.

Describe alternatives you've considered
Maintain error count channels for each HW channel

Additional context
Issue #188 and related PR #189 addressed the symptom of the failing test.