refactor(sessionresolver): adapt to changing network conditions (#238)

* feat(sessionresolver): try many and use what works

* fix(sessionresolver): make sure we can use quic

* fix: the config struct is unnecessary

* fix: make kvstore optional

* feat: write simple integration test

* feat: start adding tests

* feat: continue writing tests

* fix(sessionresolver): add more unit tests

* fix(sessionresolver): finish adding tests

* refactor(sessionresolver): changes after code review

internal/engine/internal/sessionresolver/integration_test.go

@@ -0,0 +1,29 @@
+package sessionresolver_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/internal/sessionresolver"
+)
+
+func TestSessionResolverGood(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+	reso := &sessionresolver.Resolver{}
+	defer reso.CloseIdleConnections()
+	if reso.Network() != "sessionresolver" {
+		t.Fatal("unexpected Network")
+	}
+	if reso.Address() != "" {
+		t.Fatal("unexpected Address")
+	}
+	addrs, err := reso.LookupHost(context.Background(), "google.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(addrs) < 1 {
+		t.Fatal("expected some addrs here")
+	}
+}