create mock for core-processor testing

[grishasobol]

Problem to Solve

Currently we have almost all testing in pallet_gear::tests. Actually a lot of tests will be much simpler if we will move them to core-processor, because these tests has not been created to test pallet logic, only that some cases are supported in core-processor and core-backend.

Possible Solution

Create mock for testing in core-processor

Notes

No response