Update prototypes in extension code

[myfluxi]

Fixes a few deprecation warnings such as

Return type of Tensor\Vector::getIterator() should either be compatible with
IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be
used to temporarily suppress the notice in Unknown on line 0

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[myfluxi]

I have read the CLA Document and I hereby sign the CLA

[andrewdalpino]

Hey this is great @myfluxi, I'll take a look at this ASAP

[FxNion]

Seems something is broken here ?

[myfluxi]

It is an unrelated test failing later in the process. This patch fixes some warnings which at least lets the extension compile during testing.

[mlocati]

The problem with this PR is that the code in the ext directory is automatically generated by zephir starting from the code in the tensor directory.

So, the fix should be performed in the tensor directory, like I'm suggesting in #39 (in particular, see 49f8b9e).

[andrewdalpino]

Hey thanks fellas, much appreciated! Do we still need this code since we merged @mlocati's code?

[andrewdalpino]

Closing this because I think this issue has been solved in a different PR.