fix: Blockscout and Etherscan lookups are off until the user turns them on (closes #668)

Out of the box the wallet sent the user's addresses to Blockscout and each
recipient to Etherscan. Two settings, "Use Blockscout" and "Check recipients on
Etherscan", now gate those requests. Both are off in a new install and offered
unticked on Welcome and in Settings. While one is off, the screens that relied
on it say so in a plain line. Each gated request reads its setting from storage
before it asks and when the answer lands, and drops a late answer. An open popup
takes another page's change and draws its screens again. While "Use Blockscout"
is off, no address keeps an untracked token, and no screen names a token from
Blockscout's report. ENS lookups ask only the RPC endpoint.

Model: opus-5-5

tests/unknownScaleSend.test.js

@@ -72,8 +72,12 @@ global.fetch = jest.fn(() => {
     throw new Error("tests must not perform network requests");
 });
 
+// Blockscout is asked only while the stored "Use Blockscout" is on.
 const { makeStorageStub } = require("./support/storageStub");
-global.chrome = { storage: makeStorageStub(), runtime: { sendMessage() {} } };
+global.chrome = {
+    storage: makeStorageStub({ autistmask: { useBlockscout: true } }),
+    runtime: { sendMessage() {} },
+};
 
 // A stub DOM. Every id in index.html that these two views touch resolves to a
 // fresh recording element; nothing here depends on layout, only on what the
@@ -268,6 +272,9 @@ beforeEach(() => {
     state.fraudContracts = [];
     state.hideLowHolderTokens = false;
     state.currentView = null;
+    // The screens save this page's copy of "Use Blockscout" over the stored
+    // one. So the page's copy is turned on here too.
+    state.useBlockscout = true;
 });
 
 describe("the Send screen resolves the scale rather than reading the stored one", () => {