ext/pdo: Refactor PDO::FETCH_CLASS to not rely on a FCI and use a HashTable for ctor_arg

To call the constructor we now only store the CE and a HashTable for the arguments.
This reduces the size of the _pdo_stmt_t struct from 320 bytes to 232 bytes.
Moreover, this now means that the constructor argument array follows the usual CUFA semantics.
This change is a BC break, as string keys now act like named arguments.
Moreover, the automatic wrapping of by-value arguments for by-ref parameters has been dropped, and the usual E_WARNING is now emitted in those cases.

The do_fetch() is heavily refactored to simplify the execution flow, which also makes it easier to understand.
Additionally we add a new bitflag in_fetch to prevent modification of the fetch flags by userland when PDO is fetching from the DB.

Author: Girgias

UPGRADING

@@ -50,6 +50,18 @@ PHP 8.5 UPGRADE NOTES
   . pcntl_exec() now throws ValueErrors when entries or keys of the
     $env_vars parameter contain null bytes.
 
+- PDO:
+  . The constructor arguments set in conjunction with PDO::FETCH_CLASS now
+    follow the usual CUFA (call_user_func_array) semantics.
+    This means string keys will act like a named argument.
+    Moreover, automatic wrapping for by-value arguments passed to a by-ref
+    parameter has been removed, and the usual E_WARNING about this is now
+    emitted.
+    To pass a variable by-ref to a constructor argument use the general
+    array value reference assignment: $ctor_args = [&$valByRef]
+  . Attempting to modify a PDOStatement during a call to PDO::fetch(),
+    PDO::fetchObject(), PDO::fetchAll() will now throw an Error.
+
 - PDO_FIREBIRD:
   . A ValueError is now thrown when trying to set a cursor name that is too
     long on a PDOStatement resulting from the Firebird driver.