Attempt to fix #302

What a wonderful bug we found.

I'll start from afar and take the function Assert::greaterThan($value, $limit) as an example.
The asserted condition is literally described in PHP as follows:

 $value > $limit

And when we need to describe opposite condition in which our assertion must throw an exception there are at least two ways:

• !($value > $limit) (literal)
• $value <= $limit (simple)

In the first case, the condition is described literally as the logical negation of the assertion.
In the second case, the same conditions is described, but in a more readable form using only one operand.

Its a common practice to avoid negative conditions for better readability.
So it is not surprising that many methods in this library use the second one.

Unfortunately this doesn't work with NAN.

In normal cases both form give the same result:

!($value > $limit) === $value <= $limit # true

But it doesn't work that way for NAN.
Any comparison with NAN will return false (except != and !==).
And our forms of negative condition now return different result:

!(false) === false # false

In addition to functions mentioned in issue I found 9 more assertions that lead to unexpected results when passing NAN.
I added additional test cases for those method in this PR.

Solutions

Straightforward one.
Just change the form of the negative condition from literal to simple.
This is the solution I described in this PR.

Another solution is to left simple condition but add additional checks for NAN for each of arguments.
Method to check for NAN:

protected static function isNaN($value): bool
{
    return is_float($value) && is_nan($value);
}

And the condition for Assert::greaterThan function will be:

if ($value <= $limit || self::isNaN($value) || self::isNaN($limit)) {
    static::reportInvalidArgument(\sprintf(
        $message ?: 'Expected a value greater than %2$s. Got: %s',
        static::valueToString($value),
        static::valueToString($limit)
    ));
}

This is a more readable but verbose method.

I like the second solution more. To reduce verbosity we can change check-method signature to isNaN(...$values) or atLeastOneIsNaN(...$values)