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/balances.js

@@ -9,7 +9,7 @@ const {
     formatUnits,
 } = require("ethers");
 const { ERC20_ABI } = require("./constants");
-const { log } = require("./log");
+const { log, debugFetch } = require("./log");
 const { deriveAddressFromXpub } = require("./wallet");
 
 // Use a static network to skip auto-detection (which can fail and cause
@@ -40,7 +40,7 @@ function formatTokenBalance(raw, decimals) {
 // Returns [{ address, symbol, decimals, balance }].
 async function fetchTokenBalances(address, blockscoutUrl) {
     try {
-        const resp = await fetch(
+        const resp = await debugFetch(
             blockscoutUrl + "/addresses/" + address + "/token-balances",
         );
         if (!resp.ok) {