nl: implement -d/--section-delimiter #13047

Job	Run time
Style/cargo-deny	29s
Code Coverage (ubuntu-latest, unix, nightly)	3m 42s
Code Coverage (macos-latest, macos, nightly)	3m 34s
Code Coverage (windows-latest, windows, nightly-x86_64-pc-windows-gnu)	3m 25s
Dependencies (ubuntu-latest, feat_os_unix)	19s
Documentation/warnings (ubuntu-latest, feat_os_unix)	2m 47s
Run the fuzzers	3m 38s
MinRustV (ubuntu-latest, feat_os_unix)	3m 38s
Style/deps (ubuntu-latest, feat_Tier1,feat_require_unix,feat_require_unix_utmpx)	1m 30s
Style/deps (macos-latest, feat_Tier1,feat_require_unix,feat_require_unix_utmpx)	2m 24s
Style/deps (windows-latest, feat_os_windows)	3m 12s
Style/format (ubuntu-latest, feat_os_unix)	18s
Style/lint (ubuntu-latest, feat_os_unix)	2m 33s
Style/lint (macos-latest, feat_os_macos)	3m 32s
Style/lint (windows-latest, feat_os_windows)	3m 32s
Style/spelling (ubuntu-latest, feat_os_unix)	1m 10s
toml_format	12s
Build/nightly	1s
Build/stable	1s
Build	1s
Build/Makefile	1s
Binary sizes	1s
Tests/BusyBox test suite	1s
Tests/Toybox test suite	1s
	40m 2s

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