chore: replace hardcoded stack depth with MIN_STACK_DEPTH constant

[KitaroMoha563]

Replaces magic number 16 with MIN_STACK_DEPTH constant in test helper functions.

[github-actions]

Automated check (CONTRIBUTING.md)

Findings:

• Link an issue in the PR body (e.g., "Fixes Implement SHA256 in Miden Assembly #123").
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Recommendations:

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Next steps:

• Link a relevant issue (e.g., "Fixes Implement SHA256 in Miden Assembly #123") and ensure it is assigned to you.
• See CONTRIBUTING.md for expectations.
• If this is a false positive, comment: /quality-review.

[bobbinth]

Thank you - but we do not accept PRs w/o associated issues. Also, this is now stale.