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's address to Etherscan. Two settings, "Use Blockscout" and "Check recipients on Etherscan", now gate every request that sends the user's data to those services. Both start off and are offered unticked on Welcome and in Settings. Each request reads its setting from storage before it asks. An answer that lands after the setting went off is dropped. While a setting is off, the screens that rely on it say so. ENS lookups ask only the RPC endpoint, so a name resolved off-chain does not resolve.

RULES.md's External Communication item is now out of date. Its new wording will be proposed on #211 once this lands.

Model: opus-5-5 (implementation, summary); fable-5-1 (prose)

src/shared/state.js

@@ -469,9 +469,11 @@ function mergeNetworkEndpoints(base, ours, theirs) {
 // exists to remove, just delayed and confined to one page instead of two
 // (caught by tests/txStatus.test.js). A page's live picture of a field it
 // does not own goes on being whatever its last loadState() saw, same as
-// before this fix; only the persisted record is guaranteed current. The
-// network is the exception: the popup takes a switch another context saved
-// through `beforeWrite` (followNetworkSwitch() in src/popup/index.js).
+// before this fix; only the persisted record is guaranteed current. Three
+// fields are the exceptions: the network, "Use Blockscout" and "Check
+// recipients on Etherscan". Through `beforeWrite`, the popup takes a change to
+// any of them that another context saved (followStoredSettings() in
+// src/popup/index.js).
 async function saveStateOnce(beforeWrite) {
     const result = await storageGet("autistmask");
     // The record in storage right now is about to be merged into and written
@@ -603,7 +605,7 @@ function saveState(beforeWrite) {
 }
 
 // Give this page the network switch held by `stored`, a record a save of this
-// page has just read (followNetworkSwitch() in src/popup/index.js calls this
+// page has just read (followStoredSettings() in src/popup/index.js calls this
 // from `beforeWrite`), in `state` and in `baseline` alike, as loadState() does
 // with a whole record. The switch is then not this page's own change, even when
 // that save fails to write: a later switch back to the previous network still