Refactor: Migrate from Protocols to Behaviours for Transport Layer

[joaop21]

Why:

1. Better Architecture for Service Contracts

• Protocols are designed for data polymorphism and work best with structs
• Behaviours are designed for service contracts and work best with stateful processes
• Transports are stateful services that manage connections, not data structures

2. Improved Performance

• Protocols: Runtime dispatch with potential performance overhead
• Behaviours: Direct function calls with compile-time optimization
• Transport calls happen frequently in RPC systems, so performance matters

3. Better Compile-Time Guarantees

• Protocols: Interface compliance checked at runtime
• Behaviours: Interface compliance enforced at compile time with @callback specs
• Dialyzer can catch more issues, better IDE support

4. Cleaner Dependency Management

• Before: Transports had hidden dependencies on other modules
• After: Explicit dependency injection of supervisor and registry via init_transport/2
• No more cross-module coupling or hidden dependencies

5. More Idiomatic Elixir/OTP Code

• Behaviours align with OTP philosophy of explicit, well-defined service contracts
• Better integration with supervision trees and process management
• More familiar to Elixir developers working with OTP applications