[dynamo] Support types.SimpleNamespace (#193719)

## Summary

Dynamo has no model of `types.SimpleNamespace`. Its C `tp_new` is not on the allowlist
in `UserDefinedClassVariable.supported_c_new_functions`, so constructing one
graph-breaks before anything downstream runs, and all 17 tests in
`SimpleNamespaceTests` are on the expected-failure list because of it.

The type keeps a plain instance dict and inherits `__getattribute__`, `__setattr__` and
`__delattr__` from `object`, so attribute access, `__dict__` and `vars()` come from the
existing `UserDefinedObjectVariable` machinery once construction is allowed. This adds a
`SimpleNamespaceVariable` modelling the four C slots with no Python source to inline:
`tp_init`, `tp_repr`, `tp_richcompare` and `__replace__`.

Removes 16 of the 17 expected-failure markers. `test_pickle` keeps its marker, since it
needs `_pickle.dumps`, which is on the skip list.

Draft, and no linked issue yet.

## Test Plan

    PYTORCH_TEST_WITH_DYNAMO=1 python test/cpython/v3_13/test_types.py
    python test/dynamo/test_user_defined_object.py

18 new tests ported from CPython's `SimpleNamespaceTests`, all of which fail on the
parent commit. Also ran test_repros, test_functions, test_dicts and the
repr/str/len/contains/getitem/tp_slots/tp_richcompare suites.

## Checklist

- [x] Passes lint (`lintrunner -a`)
- [x] Added/updated tests
- [ ] Updated documentation (if applicable)
- [ ] Included benchmark results (for PRs impacting perf)

## BC-breaking?

No.

---
This PR was written with the assistance of Claude (Anthropic).

Pull Request resolved: https://github.com/pytorch/pytorch/pull/193719
Approved by: https://github.com/Skylion007, https://github.com/guilhermeleobas