Propagate Connection Closed Information up to top-level (fix #465)

[sebsto]

This PR implements a mechanism to propagate connection loss information from the Lambda runtime client to the runtime loop using EventLoopFuture, enabling termination without backtrace when the connection to the Lambda control plane (or a Mock Server) is lost.

This PR depends on changes waiting approval #542
This PR fixes #465

Changes Made
Core Changes:

• LambdaRuntimeClient: Added futureConnectionClosed property to signal connection loss via EventLoopFuture
• Lambda.swift: Modified runLoop to monitor connection status and throw an error on connection loss
• LambdaRuntime and ServiceLifecycle Integration: Modified to properly handle connection loss (and other top-level) errors and avoid application to crash with a backtrace.

Termination without a backtrace

• When connection to Lambda control plane is lost, the runtime exits cleanly
• Prevents hanging or zombie processes in testing/development environments
• Maintains compatibility with AWS Lambda service behavior (new runtime environment creation)

Use Cases

• Performance Testing: Prevents hanging when testing against MockServer
• Development: Cleaner shutdown behavior during local testing
• Production: Aligns with AWS Lambda service expectations for connection loss scenarios