Random float range: different behavior from CRuby

It seems that `rand(range)` with a float range doesn't have the same understanding of an inclusive range.

With current mruby master:

```
srand(0); 1000.times.map { rand(1.0..2.0) }.select { |n| n > 2.0 }.size
 => 492
```

With Ruby 4.0.1:

```
srand(0); 1000.times.map { rand(1.0..2.0) }.select { |n| n > 2.0 }.size
=> 0
```