By not going through the Emacs decompression facilities, the annotation function
will be simpler, more robust and more efficient. The Emacs decompressor also
uses zcat/gunzip behind the scenes.

* Add marginalia-annotate-library

Needs a lot of work to make this acceptably fast. But I increasingly miss
library annotations.

* marginalia-annotate-library: Add "Loaded" indicator

Other minor improvements

* marginalia-annotate-library: Handle more library headers

Marginalia redefined the `annotation-function` in terms of the
`affixation-function` even if the `affixation-function` was not provided by
Marginalia.

Thank you, @butter71!

Now that the file annotations are usually out of sight for me thanks to
`vertico-unobtrusive-mode` it is the perfect timing to fine tune them and repair
the messed up alignment! ;)

The affixation-function is more general. This will facilitate
the following refactorings.

It is not worth the complication.