Type hints don't work with *args inside data

Coconut's `data` allows for arbitrary length constructor using the `*args` syntax, like a function, but don't allow for type hints in those.

This will work:

```python
def foo(*args: float):
```
But this won't:

```python
data foo(*args: float):
```

Coconut has built-in mypy support, so I think that syntax should be accepted (and replicated to the `__new__`, so mypy won't complain when using `--strict`).

Start by locating Coconut's handling of data constructors and its existing type-hint generation, then compare it with Python's *args annotations. Check how the constructor is replicated to __new__ and run the relevant mypy checks with --strict. Done means data foo(*args: float) is accepted and the generated code satisfies mypy.

Written by the indexing model from the issue text.