Re-organize & re-mark `url` mode tests now that they use a local server

[bskinn]

The family of tests that used to be nonlocal but now are 'network-using but local' should be differentiated from the tests that remain 'truly nonlocal' (that reach out to locations on the web).

• Create a url marker
• Split the nonlocal tests into separate test from the local-url tests
• Review/update the places where markers are used
  • Workflows
  • Local automation
  • Docs/metadata markdown (CONTRIBUTING.md, etc.)