test: the test suite exits on its own, without --forceExit (closes #585)

Some tests left timers running when they ended, and --forceExit hid them; both test scripts drop it. Six background test files left the background's 20-second timer running while an approval was pending; each now stubs it for the whole file. Five popup test files left a flash message's two-second timer running; they now use fake timers, and a wait on real zero-delay timeouts became jest.advanceTimersByTimeAsync(0). Two ethers timers can still run for up to 250 ms after a test ends; they stop before jest checks for open handles.

Model: opus-5-5

tests/sendAmountRule.test.js

@@ -131,10 +131,14 @@ async function review(amount, token) {
 async function confirm(amount, token) {
     const txInfo = await review("0.5", token);
     confirmTx.show({ ...txInfo, amount });
-    for (let i = 0; i < 10; i++) await new Promise((r) => setTimeout(r, 0));
+    for (let i = 0; i < 10; i++) await jest.advanceTimersByTimeAsync(0);
 }
 
+// showFlash() starts a timer that clears the message two seconds later. Each
+// test here runs on fake timers and drops them in afterEach, so that timer
+// never outlives the test.
 beforeEach(() => {
+    jest.useFakeTimers();
     elements.clear();
     state.wallets = [
         {
@@ -167,6 +171,10 @@ beforeEach(() => {
     state.currentView = null;
 });
 
+afterEach(() => {
+    jest.useRealTimers();
+});
+
 describe.each([
     ["1e-3", "ETH"],
     ["1e-3", "TOK"],