db: return structured errors from checkConsistency

During Open, Pebble verifies the consistency between the Version and the object
catalog. Previously if this function encountered an error or inconsistency, it
would return a new error that erased the type(s) of the original errors. This
commit modifies the function to use errors.Join and avoid the type erasure.
This is necessary for the metamorphic test's error injection, which must be
able to test an error to observe whether it is an errorfs.ErrInjected error.

Informs #1115.

open.go

@@ -1127,9 +1127,7 @@ func IsCorruptionError(err error) bool {
 }
 
 func checkConsistency(v *manifest.Version, dirname string, objProvider objstorage.Provider) error {
-	var buf bytes.Buffer
-	var args []interface{}
-
+	var errs []error
 	dedup := make(map[base.DiskFileNum]struct{})
 	for level, files := range v.Levels {
 		iter := files.Iter()
@@ -1153,22 +1151,18 @@ func checkConsistency(v *manifest.Version, dirname string, objProvider objstorag
 				size, err = objProvider.Size(meta)
 			}
 			if err != nil {
-				buf.WriteString("L%d: %s: %v\n")
-				args = append(args, errors.Safe(level), errors.Safe(fileNum), err)
+				errs = append(errs, errors.Wrapf(err, "L%d: %s", errors.Safe(level), fileNum))
 				continue
 			}
 
 			if size != int64(fileSize) {
-				buf.WriteString("L%d: %s: object size mismatch (%s): %d (disk) != %d (MANIFEST)\n")
-				args = append(args, errors.Safe(level), errors.Safe(fileNum), objProvider.Path(meta),
-					errors.Safe(size), errors.Safe(fileSize))
+				errs = append(errs, errors.Errorf(
+					"L%d: %s: object size mismatch (%s): %d (disk) != %d (MANIFEST)",
+					errors.Safe(level), fileNum, objProvider.Path(meta),
+					errors.Safe(size), errors.Safe(fileSize)))
 				continue
 			}
 		}
 	}
-
-	if buf.Len() == 0 {
-		return nil
-	}
-	return errors.Errorf(buf.String(), args...)
+	return errors.Join(errs...)
 }