Fix transaction termination handling

[StephenCathcart]

• Added a transactionState struct to hold error and callbacks that are shared with Results.
• Fixed bug in Commit by checking for tx.conn.HasFailed() before returning transactionAlreadyCompletedError.
• Removed dependency on runFailed variable by deleting it and replacing it with checks from transactionState error.
• Results throw a result failed error when trying to interact with a result that came from a transaction that errored.

[StephenCathcart]

Fix transaction handling [Go]