Review instruction cost used for simple conditional flattening

[guipublic]

Problem

PR #7205 flattens simple if statements for brillig code when it improve performance.
However the performance improvement is based on an ad-hoc estimation of the cost of each instruction.

Happy Case

We could review/fine-tune the cost function to ensure that it improves the performance

Workaround

None

Workaround Description

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Additional Context

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Project Impact

None

Blocker Context

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Would you like to submit a PR for this Issue?

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Support Needs

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