Merge multipeek peeknth#940

Draft

Owen-CH-Leung wants to merge 8 commits intorust-itertools:masterfrom

Owen-CH-Leung:merge_multipeek_peeknth

Commits on May 16, 2024

Add multipeek_general.rs
Owen-CH-Leung
committed

Commits on May 19, 2024

Change increment_index to generic add, add test to test peek_nth and peek
Owen-CH-Leung
committed