Extract readBuf #605

Job	Run time
ruby-versions / Generate Ruby versions	3s
windows-latest 3.3	2m 7s
windows-latest 3.4	52s
windows-latest 2.7	1m 40s
windows-latest 3.1	1m 10s
windows-latest 3.2	56s
windows-latest mingw	52s
windows-latest mswin	1m 0s
windows-latest 3.0	53s
windows-latest 4.0	1m 28s
windows-latest jruby-head	1m 35s
	12m 36s

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