Debug-log every API request and response

Add debugFetch wrapper in log.js that logs method, URL, and body on
request, and status code on response. Replace all fetch() calls
across balances, transactions, tokens, background RPC proxy, and
settings validation with debugFetch.

src/shared/transactions.js

@@ -7,7 +7,7 @@
 // a pure function that applies anti-poisoning heuristics.
 
 const { formatEther, formatUnits } = require("ethers");
-const { log } = require("./log");
+const { log, debugFetch } = require("./log");
 const { KNOWN_SYMBOLS } = require("./tokens");
 
 function formatTxValue(val) {
@@ -67,8 +67,8 @@ async function fetchRecentTransactions(address, blockscoutUrl, count = 25) {
     const addrLower = address.toLowerCase();
 
     const [txResp, ttResp] = await Promise.all([
-        fetch(blockscoutUrl + "/addresses/" + address + "/transactions"),
-        fetch(
+        debugFetch(blockscoutUrl + "/addresses/" + address + "/transactions"),
+        debugFetch(
             blockscoutUrl +
                 "/addresses/" +
                 address +