2947: change PyModule::add_class to return an error if class creation fails r=adamreichold a=davidhewitt
Related to #2942
At the moment there are panics deep in the `#[pyclass]` machinery when initialising the type fails. This PR adjusts a number of these functions to return `PyResult` instead, so that we can handle the error more appropriately further down the pipeline.
For example, take the following snippet:
```rust
#[pyclass(extends = PyBool)]
struct ExtendsBool;
#[pymodule]
fn pyo3_scratch(_py: Python, m: &PyModule) -> PyResult<()> {
m.add_class::<ExtendsBool>()?;
Ok(())
}
```
Currently, importing this module will fail with a panic:
```
TypeError: type 'bool' is not an acceptable base type
thread '<unnamed>' panicked at 'An error occurred while initializing class ExtendsBool', /Users/david/Dev/pyo3/src/pyclass.rs:412:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/Users/david/.virtualenvs/pyo3/lib/python3.10/site-packages/pyo3_scratch/__init__.py", line 1, in <module>
from .pyo3_scratch import *
pyo3_runtime.PanicException: An error occurred while initializing class ExtendsBool
```
After this PR, this import still fails, but with a slightly cleaner, more Pythonic error:
```
TypeError: type 'bool' is not an acceptable base type
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/Users/david/.virtualenvs/pyo3/lib/python3.10/site-packages/pyo3_scratch/__init__.py", line 1, in <module>
from .pyo3_scratch import *
RuntimeError: An error occurred while initializing class ExtendsBool
```
Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>
Co-authored-by: Adam Reichold <adam.reichold@t-online.de>
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