code: func (s StreamName) Split() (prefix, last StreamName) {
  	lidx := strings.LastIndex(string(s), StreamNameSepStr)
  	if lidx < 0 {
  		last = s
  		return
  	}
  	prefix, last = s[:lidx], s[lidx+len(StreamNameSepStr):]
  	return
  }
docs: // Split splits a StreamName on its last path element, into a prefix (everything
  // before that element) and the last element.
  //
  // Split assumes that s is a valid stream name.
  //
  // If there is only one element in the stream name, prefix will be empty.
  //
  // For example:
  //
  //	- Split("foo/bar/baz") ("foo/bar", "baz")
  //	- Split("foo") ("", "foo")
  //	- Split("") ("", "")