Fix CharuCo slowdown

[jan-jachnik-oxa]

Fixes #25188

Several functions were returning by value, rather than reference, which was creating unnecessary copies within for loops and seriously affecting the performance of Charuco detection.

Using the benchmarking app referenced in the linked issue, we can see the speed up with the changes:

Return by value

Testing new api
Number of Aruco markers detected: 204
Number of Charuco corners detected: 368
Time to detect markers: 0.053611095600000006
Time to detect charuco: 0.0427095

Return by reference:

Testing new api
Number of Aruco markers detected: 204
Number of Charuco corners detected: 368
Time to detect markers: 0.054944104199999996
Time to detect charuco: 0.0050371666

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  Patch to opencv_extra has the same branch name.
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[jan-jachnik-oxa]

The build fails on the "Compare ABI dumps" stage:

If this is a hard blocker then I think we'd have to make new functions that return by reference for use inside the detection algorithm and keep the return by value versions for backwards compatibility.