Feature: Enhance Observable Callback Coverage

[LK-Simon]

Summary

Enhance ESPressio Sockets with observable coverage for externally meaningful transport, connection and secure-session lifecycle changes.

Scope

• Expose connection/disconnection and connection-failure lifecycle notifications where applicable.
• Expose secure-session fault/reset and transport-error notifications without replacing primary data-delivery or write callbacks.
• Surface security-related lifecycle/failure observation consistently with ESPressio Security integration.
• Provide an optional ESPressio Event bridge for socket lifecycle notifications without making ESPressio Event a mandatory dependency.
• Add representative tests/examples/documentation for the observable contract and Event integration.
• Update release metadata, dependency documentation and changelog, including updated upstream dependency versions.

Compatibility

Existing socket, transport, receive and write callback APIs must remain supported. Observable/Event integration must remain optional.