Renumbering residues

Hi! Nice library, has a lot of potential.

Is there a way to renumber residues?
Renumbering atoms seems trivial (just assign a range to the atom_number), however renumbering residues would probably require some heavy duty group_by magic and could be built in.
(renumbering atoms could also be built in:)

No files or tests are named. Start by locating the DataFrame handling for atom_number and residue identifiers, then review how grouping is represented in the library. Done should include a clearly defined way to renumber residues, and possibly atoms, with behavior verified against the project’s existing structure-handling tests.

Written by the indexing model from the issue text.