Feature: do inlining of interfaces only if really needed

[oleksiyp]

Check #231 for how Channel is mocked. Besides subclassing(which is needed) MockK does inlining of a whole hierarchy of interfaces. No harm, but as well no big value.

Reducing these interfaces from instrumentation may speed up things, be less error-prone.

In case interfaces do not have any default methods they can be skipped.

[stale]

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