High CPU Usage

### Issue Details

* **Version of AdGuard Home server:**
* AdGuard Home, version v0.105.2
* **How did you install AdGuard Home:**
* Github releases
* **How did you setup DNS configuration:**
* Unbound
* **If it's a router or IoT, please write device model:**
* Installed in Oracle Cloud VM.Standard.E2.1.Micro
* **CPU architecture:**
* amd64
* **Operating system and version:**
* Ubuntu 20.04

### Expected Behavior
AGH should just block domains and answer to DNS queries via DoH and DoT.

### Actual Behavior
AGH runs fine until asked to update the filter lists, then CPU usage spikes (load on 15 minutes go over 3.00) and DNS and web interfaces become unresponsive. This behavior goes on for hours, last time I tried, it spent 5 hours like this. Looking through Github issues, found the option to pass the --no-mem-optimization parameter, which indeed made things better (load 15 min. went to 1.80) but DNS is still unresponsive.

### Additional Information
Aside from AGH, Unbound and Certbot there is nothing running in the VM. I started with AGH installed in the same Raspberry Pi 3B+ I used to Pi-hole, and when it showed the same behavior, I decided to try it on the VM, where I did a clean install and not even used the same AdGuard.yaml. Only two clients where ever connected to the VM AGH, my PC via YogaDNS and my Phone via Android Private DNS system configuration. I have around 60 filter lists (including whitelists) online that should amount to 4 to 5 million non-unique domains give or take.