Enhance wrapAsAsync to support callbacks

[czirker]

Added support for callback-style Lambda handlers in wrapAsAsync.

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Note

Low Risk
Low risk, small change isolated to wrapAsAsync to support legacy callback invocation. Main risk is subtle behavior differences if a runtime provides a callback while callers expect a Promise.

Overview
Updates wrapAsAsync to accept an optional callback argument and, when present, bypass Promise-wrapping and directly invoke the underlying handler with that callback.

When no callback is provided, it keeps the existing behavior of converting callback-style handlers into a Promise-returning async handler.

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[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Async wrapper resolves prematurely on old runtimes

High Severity

When an old Lambda runtime provides a callback, the callback != null branch does return handler(event, context, callback). Since the wrapped handlers (in cron.js, fanout.js, resource.js, test.js) are callback-style and return undefined synchronously, and the wrapper is async, the implicit Promise immediately resolves with undefined. The Lambda runtime uses this resolved Promise as the response, completing the invocation before the handler's actual work finishes and the callback is called. This causes all wrapped handlers to return undefined on Node.js 18–22 runtimes.