Replace repeats with expands

[jank324]

Description

Sub- / replacement PR for #538.

Motivation and Context

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code and checked that formatting passes (required).
• I have have fixed all issues found by flake8 (required).
• I have ensured that all pytest tests pass (required).
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• I have checked that the documentation builds (required).

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[jank324]

[jank324]

According to the benchmark, the main saving is in not doing the clone. (Event though there is still a meaningful enough saving when cloning.) So the big question is: " Where can we get away with not cloning?" I'm not perfectly sure if we can get away with that everywhere we are currently not cloning.

NOTE: The issue with not cloning is that the repeat tensors all simply view the same data, i.e. changes to one slice affect all slices.