docs: Investigate and clean up non-standard docstring formatting after PR #123

[ganow]

Follow-up from #123. Three docstring formatting issues warrant investigation and/or fixing.

bdpy/task/callback.py and bdpy/recon/torch/icnn.py — >>> inside ```python fence

In both files, doctest-style >>> lines appear inside a fenced code block:

callback.py (Examples section):

```python
>>> class Callback(BaseCallback):
...     def on_task_start(self):
...         print("Task started.")
```

icnn.py (Parameters section, inside the features description):

```python
features = {
    'conv1': np.array([...]),
}
```

What to investigate

• Does mkdocstrings/griffe correctly render bare >>> lines (without a fence) inside a Parameters description or in an Examples block?
• If bare >>> is not rendered correctly outside Examples, the fence may be an intentional workaround rather than a mistake.
• Clarify the intended rendering behavior and, if needed, move inline examples to a proper Examples section.

bdpy/mri/glm.py — missing closing quote (straightforward fix)

# current
design : 'block' or 'event_related

# should be
design : 'block' or 'event_related'