Fully explain the terse variable naming scheme in test_class_sh_property (as suggested by @rainwoodman)

Author: rwgk

.codespell-ignorelines

@@ -11,3 +11,4 @@ atyp_valu        rtrn_valu() { atyp_valu obj{"Valu"}; return obj; }
         valu = other.valu;
         with pytest.raises(ValueError) as excinfo:
     with pytest.raises(ValueError) as exc_info:
+// valu(e), ref(erence), ptr or p (pointer), r = rvalue, m = mutable, c = const,

tests/test_class_sh_property.cpp

@@ -1,3 +1,8 @@
+// The compact 4-character naming matches that in test_class_sh_basic.cpp
+// Variable names are intentionally terse, to not distract from the more important C++ type names:
+// valu(e), ref(erence), ptr or p (pointer), r = rvalue, m = mutable, c = const,
+// sh = shared_ptr, uq = unique_ptr.
+
 #include "pybind11/smart_holder.h"
 #include "pybind11_tests.h"
 
@@ -19,8 +24,6 @@ struct Field {
 };
 
 struct Outer {
-    // The compact 4-character naming matches that in test_class_sh_basic.cpp
-    // (c = const, m = mutable).
     Field m_valu;
     Field *m_mptr = nullptr;
     const Field *m_cptr = nullptr;

tests/test_class_sh_property.py

@@ -1,3 +1,6 @@
+# The compact 4-character naming scheme (e.g. mptr, cptr, shcp) is explained at the top of
+# test_class_sh_property.cpp.
+
 import pytest
 
 import env  # noqa: F401