Improve performance (Explore + Render Cache)

[Profoktor]

This PR brings down the rendering time

• from ~7s to ~3s for cached rendering
• from ~26 to ~22s for live rendering

measured on a RPi 3, running with verbose-flag

Most time-intensive tasks:

• writing to json
• reading from json
• mpstat waits for 1s (results are virtually identical when calling mpstat w/o any args)

Following changes:

• Consolidate calls to jq when exploring
• Consolidate calls to jq when rendering via cache / prepared template
  • Live Rendering cannot be optimized by this way / jq does not accept the coloring-commands
• call to mpstat w/o args when exploring CPU usage
• Additionally, the uptime is now formatted hh:mm:ss

Tests:

• [x] Debian 11 / openHABian
• [ ] Ubuntu
  • Can do, should be U2204
• [ ] RHEL
  • Don't have access to RHEL