I've played around a bit, and the issue happens when the variable
`load-history' is annotated.  At least I get the hang and 100% CPU also
when evaluating

  (marginalia-annotate-variable "load-history")

Looking at the marginalia code, I can see no evil, and indeed I can
un-marginaliarize the sample to

    (let ((print-escape-newlines t)
          (print-escape-control-characters t)
          (print-escape-multibyte t))
      (string-width (prin1-to-string load-history)))

which freezes my emacs in the same way.  Concretely, `prin1-to-string'
finishes and returns a 1.3 MB string and then `string-width' will run
indefinitely on that.  I've attached the prin1-ed value of my
load-history.