Not compatible with PHP >=7.1.0 as claimed in composer package (aka incompatible with PHP >= 8.0)

[DoItWithASmile]

I am getting the following error when using ImmArray:

Call to undefined method SplFixedArray::rewind()

An internet search revealed this change notice of PHP 8.0:

  . SplFixedArray is now an IteratorAggregate and not an Iterator.
    SplFixedArray::rewind(), ::current(), ::key(), ::next(), and ::valid()
    have been removed. In their place, SplFixedArray::getIterator() has been
    added. Any code which uses explicit iteration over SplFixedArray must now
    obtain an Iterator through SplFixedArray::getIterator(). This means that
    SplFixedArray is now safe to use in nested loops.

(source: https://github.com/php/php-src/blob/e4e2541c1a90daf708ab1ee4d44f2ab2883ce84b/UPGRADING#L515-L520)

Therefore I deduct that immutable.php is not compatible with PHP 8.0 and above, as claimed in package metadata.
(I am using the package via composer. there ">=7.1.0" is claimed)

[jkoudys]

Sorry for letting this sit. Yes this should be updated. It should be a fairly safe change. Unfortunately Iterators don't themselves implement getIterator, like you see in eg Rust implementing IntoIterator for Iterators (basically an identity). But it should be pretty easy to guard it under a version check.