Fix pointer incompatiblity
Since the subsecond part is discarded, WIDEVAL to VALUE conversion is
needed.
Some functions are not used when `THREAD_MODEL=none`
`rb_thread_sched_destroy` is not used now at all
Related issues
Bug #20447: Ruby 3.3.1 broken on i686 due to "incompatible pointer type" error
merge revision(s) 055613fd868a8c94e43893f8c58a00cdd2a81f6d,127d7a35df10ee2bc99f44b888972b2c5361d84f,e2a9b87126d59e4766479a7aa12cf7a648f46506: [Backport #20447]