Adding warning callback handlers and isAsync detection

[fabisev]

Issue #, if available:

Description of changes:

1. Added warning message for Lambda functions using callback-based handlers:

   • Warning appears when handler has 3 arguments, is not async, and is not streaming
   • Warning can be disabled by setting AWS_LAMBDA_NODEJS_DISABLE_CALLBACK_WARNING environment variable
   • Added unit tests to verify warning behavior across different handler types

2. Added detection and handling of unresolved promises in async Lambda functions:

   • Introduced NodejsExit error class with descriptive message about unresolved promises
   • Added isAsync detection to identify async Lambda handlers
   • Modified exit listener behavior to fail invocations for async handlers with unresolved promises
   • Maintained existing behavior for sync/callback handlers
   • Added unit tests to verify async handler detection

Target (OCI, Managed Runtime, both):
both

Checklist

• I have run npm install to generate the package-lock.json correctly and included it in the PR.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.