* fixed Einsum failing with repeated inputs

* Optimise the _ensure_not_equal function
Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>

* Fix einsum failing on repeated inputs

* Fix einsum failing with repeated inputs

* Added regression test for repeated inputs to the einsum function

* Fix for failing test
Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>

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Co-authored-by: Ricardo Vieira <28983449+ricardoV94@users.noreply.github.com>