refactor: dedupe provider usage auth/fetch logic and expand coverage

src/infra/provider-usage.fetch.shared.ts

@@ -16,6 +16,19 @@ export async function fetchJson(
   }
 }
 
+export function parseFiniteNumber(value: unknown): number | undefined {
+  if (typeof value === "number" && Number.isFinite(value)) {
+    return value;
+  }
+  if (typeof value === "string") {
+    const parsed = Number.parseFloat(value);
+    if (Number.isFinite(parsed)) {
+      return parsed;
+    }
+  }
+  return undefined;
+}
+
 type BuildUsageHttpErrorSnapshotOptions = {
   provider: UsageProviderId;
   status: number;