Port #7839 - Fix TLS handshake error handling

[Arkatufus]

(cherry picked from commit 1ec6f9e)

Enforce ActorSystem shutdown on TLS handshake failures

Summary

• Any TLS handshake failure now triggers CoordinatedShutdown with a clear reason (exit code 79), preventing a node from remaining "half‑healthy" via reverse connections.
• Tests cover server/client TLS failures and verify the misconfigured side shuts down.

Changes

• Transport (DotNetty)
  • Handle TlsHandshakeCompletionEvent failures in TcpTransport and run CoordinatedShutdown using a new TlsHandshakeFailureReason (exit code 79). Logs include channel endpoints and id.

New shutdown reason

• Akka.Remote.Transport.DotNetty.TlsHandshakeFailureReason (exit code 79): used by TcpTransport and EndpointManager to terminate the misconfigured system.

Tests (Akka.Remote.Tests)

• Tls_handshake_failure_should_be_logged_and_shutdown_server
• Server_side_tls_handshake_failure_should_shutdown_server
• Client_side_tls_handshake_failure_should_shutdown_client

Rationale

• Akka.NET remote is peer‑to‑peer: any TLS misconfiguration in either role must cause the association to fail hard. Shutting down the misconfigured ActorSystem avoids split‑brain‑like symptoms where nodes can still send outbound but fail inbound.

Impact / Migration

• Behavior change: nodes with TLS handshake failures now terminate (exit code 79). Ensure certificates are valid and accessible.
• No public API changes; wire protocol unaffected.

[Aaronontheweb]

LGTM