Fix typos in docstrings

### Summary
Fix typos and improve clarity in existing docstrings across the codebase.

### Tasks
- Search for common typos (e.g., "recieve", "occured", "paramter").
- Review docstrings in `src/agentunit/core/` for grammar issues.
- Fix any found issues.

### Acceptance criteria
- No obvious typos in docstrings.
- `poetry run ruff check .` passes.
