Support for `rb_io_mode_t`. #452

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-24.04 2.7	42s
ubuntu-24.04 3.0	13s
ubuntu-24.04 3.1	14s
ubuntu-24.04 3.2	14s
ubuntu-24.04 3.3	17s
ubuntu-24.04 3.4	16s
ubuntu-24.04 debug	20s
ubuntu-24.04 head	15s
ubuntu-24.04 jruby-head	59s
ubuntu-24.04 truffleruby-head	31s
ubuntu-22.04 2.7	38s
ubuntu-22.04 3.0	11s
ubuntu-22.04 3.1	14s
ubuntu-22.04 3.2	18s
ubuntu-22.04 3.3	17s
ubuntu-22.04 3.4	12s
ubuntu-22.04 debug	19s
ubuntu-22.04 head	16s
ubuntu-22.04 jruby-head	1m 9s
ubuntu-22.04 truffleruby-head	30s
	8m 8s

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