fix: a tracked token reads quantity unknown at an address no refresh has read (closes #720)

A new address, a new wallet and a network switch each leave tracked tokens
with no balance entry, so their lines read 0.0000 before any refresh had read
them.

Each of these now sets `balanceNotFetched` on the tracked tokens, and a refresh
already clears it. Their lines read `quantity unknown` until then. Addresses
that the wallet scan finds get the same. A refresh that did not read every
address the page now holds leaves the field set.

Model: opus-5-5

tests/coldWorkerChainSwitch.test.js

@@ -242,7 +242,12 @@ describe("a chain switch on a worker that never loaded state", () => {
         expect(bg.persisted().blockscoutUrl).toBe(CUSTOM_BLOCKSCOUT);
         expect(bg.persisted().wallets).toEqual(walletFixture());
         expect(bg.persisted().trackedTokens).toEqual([
-            { address: TOKEN, symbol: "DAI", decimals: 18 },
+            {
+                address: TOKEN,
+                symbol: "DAI",
+                decimals: 18,
+                balanceNotFetched: true,
+            },
         ]);
     });