Add clsas for MD_STD_STRINGS more obscure string operations

phpstan.neon

@@ -0,0 +1,12 @@
+parameters:
+    level: 8
+    bootstrapFiles:
+        - ./tests/bootstrap.php
+    paths:
+        - src
+        - tests
+    dynamicConstantNames:
+        - DATABASENAME
+        - DATABASENAME_NODA
+includes:
+    - phpstan-baseline.neon