Fix Parsing of Optional Types Annotations in DataIterableAnnotation

[clementbirkle]

This PR fixes an issue where DataIterableAnnotation couldn't correctly identify data types with optional parameters.

Previously, the test for "is data" returned:

// Previously failed
@param \Spatie\LaravelData\DataCollection<\Spatie\LaravelData\Tests\Fakes\SimpleData>|null $paramK (false)

// Previously worked
@param null|\Spatie\LaravelData\DataCollection<\Spatie\LaravelData\Tests\Fakes\SimpleData> $paramK (true)

Now, the test returns true for both cases, ensuring accurate data type identification regardless of optional parameters like |null.

[rubenvanassche]

Cool, thanks!