fix(traffic): сохранять точность объёмов и обозначать бинарные единицы

tests/e2e/traffic-observation-fixture.ts

@@ -4,6 +4,7 @@ export function observedTrafficFixturePayload(value: unknown): unknown {
   if (!value || typeof value !== "object") return value
   const r = Object.fromEntries(Object.entries(value).map(([key, v]) => [key, observedTrafficFixturePayload(v)]))
   if ("rxNow" in r && "txNow" in r && "rxTotal" in r && "txTotal" in r && Array.isArray(r.rxSeries) && Array.isArray(r.txSeries) && !("observations" in r)) {
+    r.volumeUnit = "GiB"
     r.observations = { rxNow: true, txNow: true, sampledAt: "2026-10-12T12:00:00Z",
       rxSeries: r.rxSeries.map(v => typeof v === "number" && Number.isFinite(v) && v >= 0),
       txSeries: r.txSeries.map(v => typeof v === "number" && Number.isFinite(v) && v >= 0) }