go1.24: fix lint, unit and system tests

- development env: base on debian trixie with go1.24
- lint: run with default config
- fix lint errors
- fix unit tests
- fix system test

http/http.go

@@ -12,7 +12,7 @@ type Error struct {
 	URL  string
 }
 
-// Error
+// Error returns HTTP error message
 func (e *Error) Error() string {
 	return fmt.Sprintf("HTTP code %d while fetching %s", e.Code, e.URL)
 }