all: Grand test refactor (fixes #8779, fixes #8799)

This fixes various test issues with Go 1.20.

- Most tests rewritten to use fakefs where possible
- Some tests that were already skipped, or dubious (invasive,
  unmaintainable, unclear what they even tested) have been removed
- Some actual code rewritten to better support testing in fakefs

Co-authored-by: Eric P <eric@kastelo.net>

lib/config/wrapper.go

@@ -293,6 +293,9 @@ func (w *wrapper) Serve(ctx context.Context) error {
 }
 
 func (w *wrapper) serveSave() {
+	if w.path == "" {
+		return
+	}
 	if err := w.Save(); err != nil {
 		l.Warnln("Failed to save config:", err)
 	}