Fix lint errors and bump golangci-lint to v2/action v9

- Migrate .golangci.yml to golangci-lint v2 config format
- Bump golangci-lint-action from v6 (Node 20, deprecated) to v9 (Node 24)
- Fix errcheck: check fmt.Fscanln and fmt.Sscanf return values
- Fix ineffassign: replace unused vars with _ in test files
- Fix revive unused-parameter: rename unused cmd/args/r/c params to _
- Fix revive empty-block: invert if condition in push command
- Fix revive redefines-builtin-id: rename 'clear' to 'clearsigned'
- Fix revive blank-imports: add comment on modernc.org/sqlite import
- Fix unused: remove unused 'suite' and 'gen' fields from cache entry

shared/deb/deb.go

@@ -164,7 +164,9 @@ func readAR(r io.Reader) ([]arMember, error) {
 		name = strings.TrimSuffix(name, "/")
 		sizeStr := strings.TrimSpace(string(header[48:58]))
 		var size int64
-		fmt.Sscanf(sizeStr, "%d", &size)
+		if _, err := fmt.Sscanf(sizeStr, "%d", &size); err != nil {
+			return nil, fmt.Errorf("parse ar member size %q: %w", sizeStr, err)
+		}
 		if size < 0 {
 			return nil, fmt.Errorf("negative ar member size")
 		}