test: make recovery-budget assertions independent of runner speed

[mohanagy]

User story

As a maintainer, I want recovery tests to check the order of budget decisions, so that machine load cannot turn correct recovery behavior into an assertion failure.

Acceptance criteria

• Controlled elapsed-time observations cover expiry before any pass, between passes and after the final allowed pass.
• Distinguish a completed final attempt from an attempt prevented by its budget.
• Remove the real 1 ms budget / 3 ms busy-wait race from these assertions while preserving the production recovery behavior being checked.
• Keep assertions meaningful: no skipped cases, automatic retries or global timeout increases to obtain a pass.

Scope

This is the recovery-budget slice of #710, limited to tests/unit/context-pack-recovery.test.ts and only the minimal supporting seam if needed. Implementation details remain open; no general timing or runner framework is prescribed.

Current next evidence.

The independent background-refresh timeouts, stdio-session timeouts and worker-start failures remain unresolved under #710 or their linked owners. This story cannot close those findings. It does not block the read-only branch review.

Backlog maintenance only; no coding or test run is launched by publication. Codex CLI owns any later implementation.