Fix Strict performance

[ana-pantilie]

Fixes #2439

• sum-to-n from regression-evm-... now takes ~36s compared to over 180s on master

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Review checklist

The author performs the actions on the checklist. The reviewer evaluates the work and checks the boxes as they are completed.

• Summary. Write a summary of the changes. Explain what you did to fix the issue, and why you did it. Present the changes in a logical order. Instead of writing a summary in the pull request, you may push a clean Git history.
• Documentation. Write documentation for new functions. Update documentation for functions that changed, or complete documentation where it is missing.
• Tests. Write unit tests for every change. Write the unit tests that were missing before the changes. Include any examples from the reported issue as integration tests.
• Clean up. The changes are already clean. Clean up anything near the changes that you noticed while working. This does not mean only spatially near the changes, but logically near: any code that interacts with the changes!

[ttuegel]

It seems like we need to make every binding of a SideCondition.Representation lazy. Why doesn't it work to make the type itself lazy, like this? Otherwise, we must ensure that every binding of such type is strict.