test: a failing e2e test leaves no fixture switch or send screen behind (closes #318)

A test that turns a fixture switch on for itself alone turns it off in a
finally, so a failure no longer reddens the tests after it. The two tests
that drive the popup's own send also return it to the address screen,
reopening the popup to leave a wait for a receipt. The lying-decimals()
test asserts that nothing was broadcast as soon as the send ends, before
waiting for the failure screen. ethCallResult() answers an override of 0
instead of falling back to the explorer's scale.

Model: opus-5-5

tests/e2e/network.js

@@ -256,14 +256,15 @@ const SELECTOR_DECIMALS = "0x313ce567";
 // Blockscout, which is exactly the disagreement the wallet must refuse to
 // sign over. It is read at request time, so a test flips it on the options
 // object the route was registered with — after the confirmation screen has
-// been built — without re-registering anything.
+// been built — without re-registering anything. Only null or undefined means
+// no override: 0 is a token with no decimal places, and is answered as one.
 function ethCallResult(req, opts) {
     const call = Array.isArray(req.params) ? req.params[0] : null;
     if (!call || typeof call !== "object") return ZERO_WORD;
     const data = String(call.data || call.input || "").toLowerCase();
     const to = String(call.to || "").toLowerCase();
     if (data.startsWith(SELECTOR_DECIMALS) && to === STUB_TOKEN.address) {
-        return word(opts.tokenDecimalsOverride || STUB_TOKEN.decimals);
+        return word(opts.tokenDecimalsOverride ?? STUB_TOKEN.decimals);
     }
     return ZERO_WORD;
 }
@@ -597,9 +598,10 @@ function traceEnabled(raw) {
  *   eth_estimateGas until this is cleared again.
  * @param {string[]} [opts.broadcastTransactions]  every raw signed
  *   transaction handed to eth_sendRawTransaction, appended in order.
- * @param {string} [opts.tokenDecimalsOverride]  what decimals() answers for
- *   the stub token, in place of the value Blockscout reports for it. This is
- *   the token that lies about its scale; read at request time.
+ * @param {number|string|null} [opts.tokenDecimalsOverride]  the scale
+ *   decimals() answers for the stub token, in place of the value Blockscout
+ *   reports for it; null for none, while 0 is a scale like any other. This
+ *   is the token that lies about its scale; read at request time.
  * @param {string} [opts.tokenSymbolOverride]  what the explorer reports as
  *   the stub token's symbol, in place of "E2E". This is the token whose
  *   symbol is markup; read at request time.