Adds resume functionality

[mvrsss]

Problem statement:

• Previously, there was no resume() function that would restart the consumer after cancellation.

Proposed changes:

• Implements resume() function
• Adds CANCELLING_BUT_RESUMING state to the consumer
• CANCELLING_BUT_RESUMING state is added to support prefetch update in the future
• Supports timeout in cancel and resume functions

[adamncasey]

The Doxygen CI step seems to be trying to write to this repo, which is (rightly) failing for a PR coming from a fork. I'm OK to ignore this CI check for now and someone can address the problem with this check separately