refactor: modernize Go primitives

- Replace interface{} with any (Go 1.18) across confluence/api.go,
  macro/macro.go, util/cli.go, util/error_handler.go, includes/templates.go
- Replace sort.SliceStable with slices.SortStableFunc + cmp.Compare (Go 1.21)
  in attachment/attachment.go, consistent with existing slices usage
- Replace fmt.Errorf("%s", msg) with errors.New(msg) in mark.go

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

util/error_handler.go

@@ -14,7 +14,7 @@ func NewErrorHandler(continueOnError bool) *FatalErrorHandler {
 	}
 }
 
-func (h *FatalErrorHandler) Handle(err error, format string, args ...interface{}) {
+func (h *FatalErrorHandler) Handle(err error, format string, args ...any) {
 
 	if err == nil {
 		if h.ContinueOnError {