Support for `rb_io_mode_t`. #450

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-24.04 2.7	48s
ubuntu-24.04 3.0	19s
ubuntu-24.04 3.1	25s
ubuntu-24.04 3.2	30s
ubuntu-24.04 3.3	23s
ubuntu-24.04 3.4	15s
ubuntu-24.04 debug	32s
ubuntu-24.04 head	23s
ubuntu-24.04 jruby-head	1m 14s
ubuntu-24.04 truffleruby-head	41s
ubuntu-22.04 2.7	48s
ubuntu-22.04 3.0	21s
ubuntu-22.04 3.1	19s
ubuntu-22.04 3.2	24s
ubuntu-22.04 3.3	22s
ubuntu-22.04 3.4	22s
ubuntu-22.04 debug	33s
ubuntu-22.04 head	19s
ubuntu-22.04 jruby-head	1m 16s
ubuntu-22.04 truffleruby-head	49s
	11m 6s

Provide feedback