When fully cached manifest is used, the duration used to print an
incorrect value of 55 years:
python3 -m osbuild --libdir . ./test/data/manifests/fedora-boot.json
⏱ Duration: 1753191578s
This patch fixes the duration calculation to use the correct timestamp
from the manifest by using monotonic timer instead. Additionally, it
prints nothing when there was no module executed. Finally, it improves
the formatting of the duration output.
5088c0ee69