Define #sleep in more detail

[ksss]

Defined Kernel#sleep in more detail.

Fix some problems

1. Complex inherits from Numeric, but does not accept.

$ ruby -e 'sleep 1.to_c'
-e:1:in `sleep': can't convert Complex into time interval (TypeError)
	from -e:1:in `<main>'

2. Any object that does not inherit from Numeric can be passed as an argument, as long as #divmod is defined.

https://github.com/ruby/spec/blob/1a68f6e0ffede9f0c2c6eb8c6dff75924df79d91/core/kernel/sleep_spec.rb#L25-L29

More detail

Since #divmod is defined for both Integer and Float, it could be just (_Divmod duration) -> Integer, but there are some surprises in the documentation, and I used (Integer | Float | _Divmod) in reference to CRuby implementation.

CRuby implementation is time_timespec function in time.c.

https://github.com/ruby/ruby/blob/af107710457b4bd148c6e5ee7a336ed4961f5423/time.c#L2560-L2609

There is a method File.utime that uses time_timespec function, but its behavior is not described in ruby/spec, and I've narrowed down the scope to sleep.

[soutaro]

👏