Stub: allow custom imports
These imports are written in a small DSL like:
```rust
#[pymodule(stubs = {
from datetime import datetime as dt, time;
from uuid import UUID;
})]
```
Then parsed, sent as an AST inside the introspection data (following the same AST format as the type hints) and serialized by the introspection crate that merges these imports with the auto generated ones
The `#[pymodule]` parameter is named `stub` because we might include some other features in the future like protocols