fix(monte_carlo): rehydrate nested dataclass lists when reconstructing SimConfig

[RTHYMS]

Summary

4 of 18 Monte Carlo tests fail on main with:

```
AttributeError: 'dict' object has no attribute 'volume_usd_m0'
File "token_simulator/model.py", line 195, in run
stream_volumes = [s.volume_usd_m0 for s in cfg.revenue_streams]
```

Root cause

`mc_run` round-trips `SimConfig` through `_dataclass_to_dict` and back through `_dict_to_config` to apply distribution overrides. The reconstruct step did a flat `setattr`:

```python
def _dict_to_config(d: dict) -> SimConfig:
"""Convert a flat dict back to a SimConfig (lossy — only scalar fields)."""
cfg = SimConfig()
for key, value in d.items():
if hasattr(cfg, key):
setattr(cfg, key, value)
return cfg
```

So `SimConfig.revenue_streams: List[RevenueStream]` came back as a list of dicts (one per dataclass). Then `model.run(cfg)` crashed at `s.volume_usd_m0` because `s` was a dict, not a `RevenueStream`. The docstring even admitted "lossy — only scalar fields" — but the loss was load-bearing.

Fix

Rewrite `_dict_to_config` to introspect `SimConfig`'s resolved type hints (via `typing.get_type_hints` — handles `from future import annotations` where field types are strings) and rebuild `List[]` fields by `**`-unpacking each dict back into the element type.

```python
def _dict_to_config(d: dict) -> SimConfig:
"""Convert a flat dict back to a SimConfig, rehydrating nested dataclass lists."""
field_types = get_type_hints(SimConfig)
cfg = SimConfig()
for key, value in d.items():
if not hasattr(cfg, key):
continue
item_cls = _list_item_dataclass(field_types.get(key))
if item_cls and isinstance(value, list):
value = [item_cls(**v) if isinstance(v, dict) else v for v in value]
setattr(cfg, key, value)
return cfg

def _list_item_dataclass(type_hint):
"""Return the dataclass element type for List[Foo] style hints, else None."""
if get_origin(type_hint) is list:
args = get_args(type_hint)
if args and is_dataclass(args[0]):
return args[0]
return None
```

Result

```
18 passed in 0.29s
```

(was 14 passed, 4 failed)

Drive-by

CI workflow (pytest on Python 3.11/3.12) + SECURITY.md + CI badge.

[abhicris]

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