fix: keep // comment keys with the field below them in sorted package.json sections

[dsherret]

Follow-up to #73 (#72).

#73 made a top level key starting with // travel with the field written below it. Inside the sections that are sorted alphabetically (bin, engines, the dependency sections, overrides) such a key was still sorted as an ordinary name, so it ended up at the top of the section, away from the entry it describes.

The same rule now applies in those sections: a comment key always moves with the next field.

• in a dependency section written in runs, a comment key stays in the run of the dependency below it. One written at the end of a run, with the next dependency under another heading, stays at the end of its run
• a comment key with nothing below it stays at the end of its section
• repeated "//" keys in overrides no longer count as one package named twice, which stopped the section from being sorted at all. A real duplicate still leaves it alone