Add InstanceImpl class for multi-bot support

Implement InstanceImpl class that manages multiple bots sharing a single
Federation instance. The class supports:
- Static bot creation with fixed identifier and profile
- Dynamic bot creation with dispatcher function for on-demand resolution
- Shared dispatchers that route to the correct bot based on identifier
- Inbox routing to delegate activities to the appropriate bot handlers
- Repository scanning for object ownership lookup

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: moreal