Use idiomatic error messages

- Avoid prepending "failed to..." or "error" to error messages.
- Fix typos.

pkg/parsers/starknet/hint.go

@@ -349,7 +349,7 @@ func (i *InnerDoubleDeref) UnmarshalJSON(data []byte) error {
 
  offset, ok := s[1].(float64)
  if !ok {
- return fmt.Errorf("failed to convert offset %v to float64", s[1])
+ return fmt.Errorf("convert offset %v to float64", s[1])
  }
  i.Offset = int(offset)
 
@@ -375,7 +375,7 @@ func (i *Immediate) UnmarshalJSON(data []byte) error {
 
  immediate, ok := new(big.Int).SetString(str.Immediate, 0)
  if !ok {
- return fmt.Errorf("failed to convert immediate value %s to big.Int", str.Immediate)
+ return fmt.Errorf("convert immediate value %s to big.Int", str.Immediate)
  }
 
  i.Immediate = immediate

pkg/parsers/starknet/program.go

@@ -45,13 +45,13 @@ func (b Builtin) MarshalJSON() ([]byte, error) {
  return []byte("segment_arena"), nil
 
  }
- return nil, fmt.Errorf("error marshaling builtin with unknow identifer: %d", uint8(b))
+ return nil, fmt.Errorf("marshal unknown builtin: %d", uint8(b))
 }
 
 func (b *Builtin) UnmarshalJSON(data []byte) error {
  builtinName, err := strconv.Unquote(string(data))
  if err != nil {
- return fmt.Errorf("error unmarsahling builtin: %w", err)
+ return fmt.Errorf("unmarshal builtin: %w", err)
  }
 
  switch builtinName {
@@ -74,7 +74,7 @@ func (b *Builtin) UnmarshalJSON(data []byte) error {
  case "segment_arena":
  *b = SegmentArena
  default:
- return fmt.Errorf("error unmarsahling unknwon builtin name: %s", builtinName)
+ return fmt.Errorf("unmarshal unknown builtin: %s", builtinName)
  }
  return nil
 }
@@ -106,7 +106,7 @@ func (hints *Hints) UnmarshalJSON(data []byte) error {
 
  index, ok := rawHints[0].(float64)
  if !ok {
- return fmt.Errorf("error unmarshaling hints: index should be uint64")
+ return fmt.Errorf("unmarshal hints: index should be uint64")
  }
  hints.Index = uint64(index)