[validator] improve: speed up and handle partially vds - virtual source

- now we work on caompacted urls to avoid several file opening / closing
- we look at the dataset specific virtual source and not all sources.
  This is handled only at level 1. Not at virtual source src_space
4 jobs for add_validator in 6 minutes and 32 seconds (queued for 25 seconds)
Status Name Job ID Coverage
  Build
passed check_style #248563

00:00:10

 
  Test
passed test:python3.7_stretch_pyqt5 #248564

00:05:44

82.0%
passed test:python3.9_stretch_pyqt5 #248565

00:06:21

82.0%
passed test:test-tomoscan-tutorials #248566

00:05:04