Improve quality and tracing of license detection in Debian copyright files

1. we should be able to recover from mostly OK but not correct copyright files such as this one: https://metadata.ftp-master.debian.org/changelogs//main/p/pulseaudio/pulseaudio_14.2-1_copyright (this may be a ticket for the debian-inspector debut library though)
See https://github.com/nexB/debut/issues/6 Recover parsing from almost machine-readable copyright files

2. we should have the ability to trace the intermediate detection results (see also #2389 ) for each paragraph of a copyright file
3. we could establish a mapping of declared License "ids"
4. there is an implicit notion of primary vs. secondary licenses in a copyright file and we should leverage this: a paragraph with "Files: *" applies to the package as a whole. This may mean a system-wide model change to track primary vs. secondary license or have the ability to track that in a license expression. See https://github.com/nexB/debut/issues/8 Determine the primary license from a copyright file