Refactord Concept class to regroup all builtins properties into a ConceptMetadata class

tests/test_builtin_helpers.py

@@ -25,7 +25,7 @@ def test_i_can_use_expect_one_when_too_many_success():
     res = core.builtin_helpers.expect_one(get_context(sheerka), items)
     assert not res.status
     assert sheerka.isinstance(res.value, BuiltinConcepts.TOO_MANY_SUCCESS)
-    assert res.value.obj == items
+    assert res.value.body == items
     assert res.parents == items
 
 
@@ -51,7 +51,7 @@ def test_i_can_use_expect_when_only_errors_1():
     res = core.builtin_helpers.expect_one(get_context(sheerka), items)
     assert not res.status
     assert sheerka.isinstance(res.value, BuiltinConcepts.TOO_MANY_ERRORS)
-    assert res.value.obj == items
+    assert res.value.body == items
     assert res.parents == items
 
 
@@ -65,7 +65,7 @@ def test_i_can_use_expect_when_only_errors_2():
     res = core.builtin_helpers.expect_one(get_context(sheerka), items)
     assert not res.status
     assert sheerka.isinstance(res.value, BuiltinConcepts.TOO_MANY_ERRORS)
-    assert res.value.obj == items
+    assert res.value.body == items
     assert res.parents == items