Refactor into MappingStrategy class and fix recursive mapping (#3)

* Refactor into MappingStrategy class and fix recursive mapping

* Improve PHP 7.4 compatibility

* Adjust CI config

Author: bancer

.github/workflows/ci.yml

@@ -36,6 +36,7 @@ jobs:
       matrix:
         include:
           # ORM 4 requires PHP >= 7.2
+            # Entity fields are not casted to integers in PHP 7.4 and 8.0
           - { php: '7.4', orm: '4' }
           - { php: '8.0', orm: '4' }
           - { php: '8.1', orm: '4' }