cat: Improve performance of formatting. #6999

Job	Run time
Style/format (ubuntu-latest, feat_os_unix)	20s
Style/lint (macos-latest, feat_os_macos)	56s
Style/spelling (ubuntu-latest, feat_os_unix)	2m 28s
Style/lint (ubuntu-latest, feat_os_unix)	43s
Style/toml	10s
Style/lint (windows-latest, feat_os_windows)	2m 17s
Style/Python	9s
	7m 3s

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