Add a TODO about refactoring critical sections

Author: emmatyping

Modules/_zstd/compressor.c

@@ -134,6 +134,7 @@ _get_CDict(ZstdDict *self, int compressionLevel)
     PyObject *capsule;
     ZSTD_CDict *cdict;
 
+    // TODO(emmatyping): refactor critical section code into a lock_held function
     Py_BEGIN_CRITICAL_SECTION(self);
 
     /* int level object */