Add support for Python's "Limited API"; Test cibuildwheel and py >=3.5 using TestPythonSML.py

Core/ClientSMLSWIG/Python/Python_sml_ClientInterface.i

@@ -11,6 +11,10 @@
 // handle windows calling convention, __declspec(dllimport), correctly
 %include <windows.i>
 
+%begin %{
+#define Py_LIMITED_API 0x03050000
+%}
+
 %{
 	// helps quell warnings
 	#ifndef unused
@@ -252,7 +256,10 @@
 			return "";
 		}
 
-		std::string res = PyUnicode_AsUTF8 (result);
+		PyObject* unicode = PyUnicode_AsUTF8String (result);
+		std::string res = PyBytes_AsString(unicode);
+
+		Py_DECREF(unicode);
 		Py_DECREF(result);
 
 		PyGILState_Release(gstate); /* Release the thread. No Python API allowed beyond this point. */
@@ -303,7 +310,10 @@
 			return "";
 		}
 
-		std::string res = PyUnicode_AsUTF8 (result);
+		PyObject* unicode = PyUnicode_AsUTF8String (result);
+		std::string res = PyBytes_AsString(unicode);
+
+		Py_DECREF(unicode);
 		Py_DECREF(result);
 
 		PyGILState_Release(gstate); /* Release the thread. No Python API allowed beyond this point. */

Core/ClientSMLSWIG/Python/pyproject.toml

@@ -70,7 +70,7 @@ requires = [
     # and other python build/install frontends (such as pip itself).
     #
     # We use a forked version of enscons to add python 3.12 support.
-    "enscons @ git+https://github.com/ShadowJonathan/enscons-soar@544f39f",
+    "enscons @ git+https://github.com/ShadowJonathan/enscons-soar@190091866ac35fb5d390c425bafaf13443baee5e",
 
     # Required sub-dependencies of enscons.
     "toml>=0.1",

SConstruct

@@ -417,11 +417,13 @@ py_sources += [
 env.Alias(SML_PYTHON_ALIAS + "_dev", py_sources)
 
 if enscons_active:
-    env['PACKAGE_METADATA'] = enscons.get_pyproject(env)['project']
     # Instead of giving an explicit tag, we tell enscons that we're not building a "pure" (python-only) library,
     # and so we let it determine the wheel tag by itself.
     env['ROOT_IS_PURELIB'] = False
 
+    # This enables tagging the wheel with the limited api, and also sets the target python version.
+    env["LIMITED_API_TARGET"] = (3, 5)
+
     # Whl and WhlFile add multiple targets (sdist, dist_info, bdist_wheel, editable) to env
     # for enscons (python build backend for scons; required for building with cibuildwheel).
     whl = env.Whl("platlib", py_sources, root="")