port 2P step 1: vendor CPython 2.7.18 as the mtpython static library

The embedded 40250 script layer needs its own interpreter on five platforms.
2.7 is end-of-life, so nothing can be fetched from the target SDKs and the
source is vendored (official 2.7.18 tarball, trimmed to 25MB; Lib/ stays for
step 3's python27.zip).

cpython-2.7.18/CMakeLists.txt builds one `mtpython` static library from exactly
the 133 objects the reference libpython2.7.a contains, off by default behind
-DMTGODOT_EMBED_PYTHON=ON. The source list and the built-in module table
(config/config.c, 39 entries) are shared; pyconfig.h is a probe result and is
not, so each platform keeps its own under config/<platform>/, regenerated by
tools/py_embed/gen_pyconfig.sh and checked against the shared table.

Three vendor patches, documented in docs/THIRD-PARTY.md: configure/configure.ac
learn arm64 on macOS, and posixmodule.c undefines the process-control calls it
hard-defines past pyconfig.h when building for iOS.

macOS (ctest python.embed: every builtin imports, codecs and pickle work off the
vendored Lib/), Android arm64 and iOS arm64 build. Linux needs a Linux host and
Windows needs a MinGW-vs-MSVC decision; both are noted for step 4.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/third_party/cpython-2.7.18/Modules/timingmodule.c

@@ -0,0 +1,62 @@
+/*
+ * Author: George V. Neville-Neil
+ */
+
+#include "Python.h"
+
+/* Our stuff... */
+#include "timing.h"
+
+static PyObject *
+start_timing(PyObject *self)
+{
+    Py_INCREF(Py_None);
+    BEGINTIMING;
+    return Py_None;
+}
+
+static PyObject *
+finish_timing(PyObject *self)
+{
+    ENDTIMING
+    Py_INCREF(Py_None);
+    return Py_None;
+}
+
+static PyObject *
+seconds(PyObject *self)
+{
+    return PyInt_FromLong(TIMINGS);
+}
+
+static PyObject *
+milli(PyObject *self)
+{
+    return PyInt_FromLong(TIMINGMS);
+}
+
+static PyObject *
+micro(PyObject *self)
+{
+    return PyInt_FromLong(TIMINGUS);
+}
+
+
+static PyMethodDef timing_methods[] = {
+    {"start",   (PyCFunction)start_timing, METH_NOARGS},
+    {"finish",  (PyCFunction)finish_timing, METH_NOARGS},
+    {"seconds", (PyCFunction)seconds, METH_NOARGS},
+    {"milli",   (PyCFunction)milli, METH_NOARGS},
+    {"micro",   (PyCFunction)micro, METH_NOARGS},
+    {NULL,      NULL}
+};
+
+
+PyMODINIT_FUNC inittiming(void)
+{
+    if (PyErr_WarnPy3k("the timing module has been removed in "
+                        "Python 3.0; use time.clock() instead", 2) < 0)
+        return;
+
+    (void)Py_InitModule("timing", timing_methods);
+}