Add PY public API and base classes

Introduces main Python Interface entry points:
- ClivePy: For read-only operations without profile (show.profiles())
- UnlockedClivePy: For operations requiring unlocked profile
- clive_use_unlocked_profile(): Factory function for UnlockedClivePy
- PyWorld: World specialized for PY usage with automatic profile loading

High-level interfaces:
- ShowInterface: balances, accounts, witnesses, authority methods
- ShowInterfaceNoProfile: profiles listing
- GenerateInterface: random key generation
- ConfigureInterface: profile configuration

Public API available via: from clive.py import ClivePy, UnlockedClivePy

Note: Process operations (transfer, update_authority) are stubbed
with NotImplementedError - will be implemented in part2.