Extend cost guardrails with forecasts and notification coverage

What

Extend costguardrails with two account-level checks: budgets forecast to breach their limit, and budgets or Cost Anomaly Detection monitors that cannot notify anyone.

Why

The current rules detect missing guardrails and budgets that have already exceeded their limit. They do not catch a likely breach early, or a guardrail that exists but has no working notification path.

Details

• Normalize forecasted budget spend, budget notifications, notification subscribers, anomaly subscriptions, and subscriber status in the SDK.
• Flag a forecasted breach only when the forecast and budget use the same unit and the forecast is above the configured limit.
• Flag budgets without enabled subscribers and anomaly monitors without an active subscription that references them.
• Keep malformed, unavailable, and unit-mismatched data out of findings and surface access failures as diagnostics.
• Discovery only. Continue the CLDBRN-AWS-COSTGUARDRAILS-N sequence.

Start with the costguardrails SDK and trace how forecasted spend, budget notifications, notification subscribers, anomaly subscriptions, and subscriber status are normalized. Follow the existing account-level checks in the CLDBRN-AWS-COSTGUARDRAILS-N sequence. Done means discovery findings cover only valid, matching data while malformed or unavailable data becomes diagnostics.