[FEATURE]: API endpoint for Go plan usage metrics (rolling/weekly/monthly)

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Problem

There's no programmatic way to check Go plan usage metrics (5-hour rolling, weekly, monthly). Currently only available via the web console at /workspace/:id/go.

Proposed solution

Add a REST endpoint (or SDK method) that returns:

• rollingUsage: { usagePercent, resetInSec, limit }
• weeklyUsage: { usagePercent, resetInSec, limit }
• monthlyUsage: { usagePercent, resetInSec, limit }

Use case

Automated monitoring, dashboards, CLI tools that need to check Go usage without browser login.