js-yaml: YAML merge-key chains can force quadratic CPU consumption

Impact js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly. The issue is triggered by a chain of mappings where each mapping merges the previous one: yaml a0: &a0 k0: 0 a1: &a1 1s doc size 100K js import performance from 'node:perfhooks' import Buffer from...