Returns 'sections' in order, each {identifier, heading}, with
type='appendix' on appendices (2 CFR 200's Appendix I-XII, for example)
and reserved=true on reserved sections, plus 'subparts' (each with its
heading, section_count and first and last section). Useful for seeing
the scope of a part before reading specific sections.

The part number alone is enough: chapter is optional (Title 48 parts
are unique: 52 = FAR, 252 = DFARS, 552 = GSAR) and the answer reports
the chapter the part is in. subpart (e.g. '52.2') lists one subpart.
A list too long to send at once (FAR Part 52 has 680 entries) comes in
pages: page and total_pages say where you are; page=2 gets the rest.
detail=True adds eCFR's label, size and received_on for each entry
(received_on is when eCFR processed the text, not when it was amended;
get_version_history has amendment dates).

part_number accepts int or string.