Fix Issue 24541 - cartesianProduct should have a length for finite ranges

[nicolo-mn]

This Draft PR aims to address issue #9871 (Issue 24541 on BugZilla). As of now, I have added a length field to the cartesianProduct implementation with two finite forward ranges. Since I've already built the unittests for it I'm publishing this Draft PR in case anyone wants to give some feedback. I'm still working on the case of two finite ranges where one of them is not a forward range, particularly to replace the joiner returned in cartesianProduct with a sized range.

Changelog as of now:

• Modified the Result struct inside cartesianProduct to include a length field.
• Added checks on length in unittest regarding cartesianProduct with finite forward ranges.
• Added a unittest to ensure the correct calculation of length when popping elements.

[dlang-bot]

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Testing this PR locally

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dub run digger -- build "master + phobos#10657"

[nicolo-mn]

length field in cartesianProduct with one finite input range and one finite forward range has been added

[nicolo-mn]

@thewilsonator Could you check my changes when you got some time? Thanks in advance!