itest: add wallet_synced field integration test

In this commit, we add an integration test that verifies the
wallet_synced field in GetInfoResponse correctly reflects the wallet's
sync state.

The test creates a node, verifies wallet_synced becomes true after
initial sync, then stops the node and mines blocks while it's offline.
After restart, the test polls GetInfo to observe the wallet catching up,
ideally capturing the transition from wallet_synced=false to true.

The test is registered in the "wallet sync" test case group.

itest/list_on_test.go

@@ -842,6 +842,9 @@ func init() {
 	allTestCases = appendPrefixed(
 		"wallet", allTestCases, walletTestCases,
 	)
+	allTestCases = appendPrefixed(
+		"wallet sync", allTestCases, walletSyncTestCases,
+	)
 	allTestCases = appendPrefixed(
 		"coop close with external delivery", allTestCases,
 		coopCloseWithExternalTestCases,