Reduce runtime of spec/requests/datacite_dois_spec.rb

[jrhoads]

requests/datacite_dois_spec.rb has been identified in #1241 as one of the specs that is taking the most overall clock time. Which has the knock-on effect of slowing the overall test suite down. Let's see if we can reduce the runtime of this spec.

Current runtime in CI is about 14 minutes.

The file has ~5k lines of code in the spec and has several sleep statements in it.

These are places where we can focus:

• Perhaps split the spec into multiple smaller specs
• See if we can remove sleep statements and still retain functional coverage.