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/addressScanCancelled.test.js

@@ -44,6 +44,7 @@ jest.doMock("../src/popup/views/helpers", () => ({
     goBack: () => {},
     clearViewStack: () => {},
     onViewLeave: () => {},
+    markTrackedTokensNotFetched: () => {},
 }));
 
 // state.js reads chrome.storage.local at load, and saveState() writes it.