chore(deps): add pybind11

.gitmodules

@@ -28,3 +28,6 @@
 [submodule "third_party/cpuinfo"]
 	path = third_party/cpuinfo
 	url = https://github.com/pytorch/cpuinfo.git
+[submodule "third_party/pybind11"]
+	path = third_party/pybind11
+	url = https://github.com/pybind/pybind11.git

third_party/prepare.sh

@@ -36,3 +36,5 @@ pushd MegRay/third_party >/dev/null
     git submodule update --init gdrcopy
     git submodule update --init ucx
 popd >/dev/null
+
+git submodule update --init pybind11

third_party/pybind11

@@ -0,0 +1 @@
+Subproject commit b3d8fec066285c831b69fd77c092f1cc70e38882