### What problem does this PR solve?
Introduced [beartype](https://github.com/beartype/beartype) for runtime
type-checking.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
The default value of Python function parameters cannot be mutable.
Modifying this parameter inside the function will permanently change the
default value
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
