Unit Test Coverage for Sync Subtensor

[thewhaleking]

Unit Test coverage for the synchronous subtensor class in the Bittensor SDK is currently 42%. We need to bring this to 80%

AC:

• Unit test coverage for bittensor/core/subtensor.py class is >= 80%

[basfroman]

This task will be implemented after PR #2526 is done and merged.

[zyzniewski-reef]

#2713