Port some internal streams tests to wd-test format

[jasnell]

Had claude port a handful of the easier-to-port tests and provide a checklist for doing the rest. Some will require manual figuring out to port, most likely can be automated with claude.

PR is tests and doc only. No functional changes. As long as CI passes they should be good. Once existing tests have been ported, a separate analysis of test coverage will be performed to determine what is missing.