ax(mining): replace banned errors import with ErrInternal in mining_profile.go

RawConfig.UnmarshalJSON used errors.New() (banned import) despite the
package already providing ErrInternal() for exactly this purpose.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/mining_profile.go

@@ -1,8 +1,5 @@
 package mining
 
-import (
-	"errors"
-)
 
 // RawConfig is a raw encoded JSON value.
 // It implements Marshaler and Unmarshaler and can be used to delay JSON decoding or precompute a JSON encoding.
@@ -29,7 +26,7 @@ func (m RawConfig) MarshalJSON() ([]byte, error) {
 // if err := json.Unmarshal(raw, &profile.Config); err != nil { ... }
 func (m *RawConfig) UnmarshalJSON(data []byte) error {
 	if m == nil {
-		return errors.New("RawConfig: UnmarshalJSON on nil pointer")
+		return ErrInternal("RawConfig: UnmarshalJSON on nil pointer")
 	}
 	*m = append((*m)[0:0], data...)
 	return nil