fix: FoldingRules.toString to print markers #1372

Job	Run time
build (ubuntu-latest, oldest)	2m 6s
build (ubuntu-latest, latest)	2m 19s
build (ubuntu-latest, unstable)	2m 7s
build (macos-13, oldest)	3m 14s
build (macos-13, latest)	3m 10s
build (macos-13, unstable)	2m 57s
build (macos-14, oldest)	1m 50s
build (macos-14, latest)	2m 13s
build (macos-14, unstable)	1m 59s
build (windows-latest, oldest)	2m 29s
build (windows-latest, latest)	3m 3s
build (windows-latest, unstable)	2m 43s
	30m 10s

Provide feedback