Simplify interface checking with type assertions

Replace reflect.Type.Implements() with type assertion using comma-ok
idiom and remove redundant pointer interface check. The recursive
decode call handles pointer receiver implementations via CanAddr().

Eliminates unmarshalerType variable and reduces code complexity while
maintaining identical functionality and performance.

Author: oschwald

internal/decoder/reflection.go

@@ -17,9 +17,6 @@ type Unmarshaler interface {
 	UnmarshalMaxMindDB(d *Decoder) error
 }
 
-// unmarshalerType is cached for efficient interface checking.
-var unmarshalerType = reflect.TypeFor[Unmarshaler]()
-
 // ReflectionDecoder is a decoder for the MMDB data section.
 type ReflectionDecoder struct {
 	DataDecoder
@@ -245,30 +242,17 @@ func (d *ReflectionDecoder) decode(offset uint, result reflect.Value, depth int)
 	}
 
 	// First handle pointers by creating the value if needed, similar to indirect()
-	// but we don't want to fully indirect yet as we need to check for Unmarshaler
 	if result.Kind() == reflect.Ptr {
 		if result.IsNil() {
 			result.Set(reflect.New(result.Type().Elem()))
 		}
-		// Now check if the pointed-to type implements Unmarshaler using cached type check
-		if result.Type().Implements(unmarshalerType) {
-			unmarshaler := result.Interface().(Unmarshaler) // Safe, we know it implements
-			decoder := NewDecoder(d.DataDecoder, offset)
-			if err := unmarshaler.UnmarshalMaxMindDB(decoder); err != nil {
-				return 0, err
-			}
-			return decoder.getNextOffset()
-		}
-		// Continue with the pointed-to value
+		// Continue with the pointed-to value - interface check will happen in recursive call
 		return d.decode(offset, result.Elem(), depth)
 	}
 
-	// Check if the value implements Unmarshaler interface
-	// We need to check if result can be addressed and if the pointer type implements Unmarshaler
+	// Check if the value implements Unmarshaler interface using type assertion
 	if result.CanAddr() {
-		ptrType := result.Addr().Type()
-		if ptrType.Implements(unmarshalerType) {
-			unmarshaler := result.Addr().Interface().(Unmarshaler) // Safe, we know it implements
+		if unmarshaler, ok := result.Addr().Interface().(Unmarshaler); ok {
 			decoder := NewDecoder(d.DataDecoder, offset)
 			if err := unmarshaler.UnmarshalMaxMindDB(decoder); err != nil {
 				return 0, err