Analyzer::Go::Gf

One precompiled matcher instead of a String#includes? scan per .go file: includes? runs Rabin-Karp over the whole buffer and the marker is absent in the overwhelming majority of files in a polyglot repo, so every one of them pays the full scan. See Analyzer#content_matches?.

Instance-side view of the same declaration. The per-file rescues live on this base class, which has no way to name the analyzer that is running inside them, so a skipped file could not be attributed to a tech. Deriving it from analyzer_for keeps the name written exactly once.