fix: revalidate usage on get

[kaposke]

Ensure UsageTracker revalidates stale or missing cache entries on reads

Updates UsageTracker so that both get and getAll initiate revalidate when cache entries are missing or have exceeded revalidateAfter, keeping read paths consistent with the existing incr behavior. Adds integration tests covering null, stale, and fresh cache scenarios for get/getAll, using spies to assert revalidation triggers and fake timers to simulate staleness windows.

Key Changes

• Invoke revalidate from UsageTracker.get when entry.value is null or stale
• Invoke revalidate per metric inside UsageTracker.getAll under the same conditions
• Extend packages/account-usage/lib/usage.integration.test.ts with coverage for get and getAll revalidation behaviors using vi timers and spies

Affected Areas

• packages/account-usage/lib/usage.ts
• packages/account-usage/lib/usage.integration.test.ts

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📊 2 files reviewed • 4 need attention

⚠️ Needs Attention:

• packages/account-usage/lib/usage.ts — The changes affect sensitive user account data tracking with significant logic changes concerning data revalidation.

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[TBonnin]

can we add/modify tests to check the new behavior

[TBonnin]

how can value be null?