SW-117 — Add doctor runtime benchmark with fake executables

[dDevAhmed]

Summary

Measure doctor runtime deterministically using controlled fake executables and bounded timeout behavior.

Acceptance Criteria

• benchmark does not depend on installed tools/network;
• timeout path is represented;
• regressions can be compared without flaky hard timing;
• repository checks pass.

Dependencies

• SW-030

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🏷 Labels

• Stellar Wave
• type: performance
• area: diagnostics
• priority: P2
• difficulty: medium
• points: 150
• workstream: performance