Support for `rb_io_mode_t`. #449

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 2.7	46s
ubuntu-24.04 3.0	21s
ubuntu-24.04 3.1	21s
ubuntu-24.04 3.2	27s
ubuntu-24.04 3.3	20s
ubuntu-24.04 3.4	11s
ubuntu-24.04 debug	28s
ubuntu-24.04 head	19s
ubuntu-24.04 jruby-head	1m 23s
ubuntu-24.04 truffleruby-head	43s
ubuntu-22.04 2.7	50s
ubuntu-22.04 3.0	23s
ubuntu-22.04 3.1	29s
ubuntu-22.04 3.2	23s
ubuntu-22.04 3.3	24s
ubuntu-22.04 3.4	20s
ubuntu-22.04 debug	27s
ubuntu-22.04 head	21s
ubuntu-22.04 jruby-head	1m 17s
ubuntu-22.04 truffleruby-head	42s
	10m 59s

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