Support for `rb_io_mode_t` (#129) #394

Job	Run time
ruby-versions / Generate Ruby versions	2s
windows-latest 2.7	2m 18s
windows-latest 3.0	2m 29s
windows-latest 3.1	1m 48s
windows-latest 3.2	2m 36s
windows-latest 3.3	2m 3s
windows-latest 3.4	2m 25s
windows-latest jruby-head	1m 38s
windows-latest mingw	1m 45s
windows-latest mswin	1m 38s
	18m 42s

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