Enable users to ask what is the untrimmed or trimmed length of SeqRecord object holding e.g. SFF data. Add a placeholder for a method whichj would apply annotated trim points of requested types over the current SeqRecord instance. Improve an error message when user changes annotation dictionary and the change results in a different length compared to current one (which is not allowed). More information at https://redmine.open-bio.org/issues/3437