Better error handling

[flcl42]

The core can handle exceptions, connection issues, protocol errors much better. Potential improvements:

• [x] Add dotnet-libp2p specific exceptions for issues appeared during stack building, setting up connection, regular protocol work
• [x] Add simple reconnection API, consider circuit breaker pattern
• [ ] Confirm exceptions are passed from session protocols to the caller
• [ ] Confirm broken session is traceable if failure appears on transport/connection level