Return partial results in the condition on interrupt

[gaborcsardi]

Closes #98.

[hadley]

Did you consider just switching to req_perform_iterative() so you could inherit from httr2?

[gaborcsardi]

Yeah, I looked at that solution. But it does not seem like a good idea to me to ignore interrupts and return partial results downstream. I think if the user presses an interrupt in an interactive session or sends a SIGINT to a worker subprocess then they want the computation/worker stopped. This is essentially the same concert you had in the issue, hence your top-level restriction suggestion. I think this PR essentially implements that at the top level and has more predictable behavior, i.e. an interrupt will jump to top level.