add atomic SetNX cache operation

Split the memory and Redis cache implementations into separate files and
provide backend-native atomic set-if-absent support.

management/server/cache/memory_test.go

@@ -0,0 +1,49 @@
+package cache_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/netbirdio/netbird/management/server/cache"
+)
+
+func TestMemoryStore(t *testing.T) {
+	memStore, err := cache.NewStore(context.Background(), 100*time.Millisecond, 300*time.Millisecond, 100)
+	if err != nil {
+		t.Fatalf("couldn't create memory store: %s", err)
+	}
+	ctx := context.Background()
+	key, value := "testing", "tested"
+	err = memStore.Set(ctx, key, value)
+	if err != nil {
+		t.Errorf("couldn't set testing data: %s", err)
+	}
+	result, err := memStore.Get(ctx, key)
+	if err != nil {
+		t.Errorf("couldn't get testing data: %s", err)
+	}
+	if value != result.(string) {
+		t.Errorf("value returned doesn't match testing data, got %s, expected %s", result, value)
+	}
+	created, err := memStore.SetNX(ctx, "atomic", value, 100*time.Millisecond)
+	if err != nil {
+		t.Fatalf("couldn't atomically set testing data: %s", err)
+	}
+	if !created {
+		t.Fatal("first atomic set should create the entry")
+	}
+	created, err = memStore.SetNX(ctx, "atomic", value, 100*time.Millisecond)
+	if err != nil {
+		t.Fatalf("couldn't atomically check testing data: %s", err)
+	}
+	if created {
+		t.Fatal("second atomic set should not replace the entry")
+	}
+	// test expiration
+	time.Sleep(300 * time.Millisecond)
+	_, err = memStore.Get(ctx, key)
+	if err == nil {
+		t.Error("value should not be found")
+	}
+}