[BE] Correctly pass exceptions raised from rpc_init to CPython (pytorch#154325)

By decorating function body with `HANDLE_TH_ERRORS`

Partially addresses pytorch#154300

I.e. after that change, importing torch no longer crashes but returns a readable (and actionable exception)
```
>>> import torch
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import torch
  File "/Users/malfet/git/pytorch/pytorch/torch/__init__.py", line 2134, in <module>
    from torch import _VF as _VF, functional as functional  # usort: skip
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/malfet/git/pytorch/pytorch/torch/functional.py", line 8, in <module>
    import torch.nn.functional as F
  File "/Users/malfet/git/pytorch/pytorch/torch/nn/__init__.py", line 8, in <module>
    from torch.nn.modules import *  # usort: skip # noqa: F403
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/malfet/git/pytorch/pytorch/torch/nn/modules/__init__.py", line 2, in <module>
    from .linear import Bilinear, Identity, LazyLinear, Linear  # usort: skip
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/malfet/git/pytorch/pytorch/torch/nn/modules/linear.py", line 7, in <module>
    from torch.nn import functional as F, init
  File "/Users/malfet/git/pytorch/pytorch/torch/nn/functional.py", line 11, in <module>
    from torch._jit_internal import (
    ...<5 lines>...
    )
  File "/Users/malfet/git/pytorch/pytorch/torch/_jit_internal.py", line 42, in <module>
    import torch.distributed.rpc
  File "/Users/malfet/git/pytorch/pytorch/torch/distributed/rpc/__init__.py", line 37, in <module>
    from torch._C._distributed_rpc import (  # noqa: F401
    ...<33 lines>...
    )
ImportError: cannot import name '_DEFAULT_NUM_WORKER_THREADS' from 'torch._C._distributed_rpc' (unknown location)

```

Pull Request resolved: pytorch#154325
Approved by: https://github.com/Skylion007

Author: malfet

torch/csrc/distributed/rpc/init.cpp

@@ -30,6 +30,7 @@ template <typename T>
 using shared_ptr_class_ = py::class_<T, std::shared_ptr<T>>;
 
 PyObject* rpc_init(PyObject* _unused, PyObject* noargs) {
+  HANDLE_TH_ERRORS
   auto rpc_module =
       THPObjectPtr(PyImport_ImportModule("torch.distributed.rpc"));
   if (!rpc_module) {
@@ -845,6 +846,7 @@ PyObject* rpc_init(PyObject* _unused, PyObject* noargs) {
   module.def("_disable_jit_rref_pickle", &disableJitRRefPickle);
 
   Py_RETURN_TRUE;
+  END_HANDLE_TH_ERRORS
 }
 
 } // namespace