The 20-operation xcrun simctl surface. The Rust analogue of Swift’s
SimctlClient protocol witness: a trait rather than a struct-of-closures,
since Rust traits give the same live/mock seam without closure-capture
boilerplate.
Builds the argv for simctl io <udid> recordVideo. Only constructs the
command — spawning and owning the child process is Recorder’s job,
because the SIGINT-to-finalize semantics live there.