Augment Driver class with error handling via RetryInvoker

[panh99]

• Added a sync lock for Driver API calls in the Driver class to prevent potential thread conflicts
• Wrapped all Driver API calls within RetryInvoker.
• Added new unit tests in driver/driver_test.py

The default RetryInvoker for the Driver class is configured as follows.

err_codes = (StatusCode.UNAVAILABLE,)
RetryInvoker(
    exponential,
    RpcError,
    max_tries=10,
    max_time=300,
    should_giveup=lambda e: e.code() not in err_codes,
)