Feature request: add async api adapter for async resolver support

[leandrodamascena]

Use case

_registered_api_adapter is the final middleware in the chain - it calls the actual route handler with the correct arguments. Today it's synchronous and can't await async handlers. We need an async version that detects coroutines and awaits them.

Solution/User Experience

• Add _registered_api_adapter_async() function that:
  • Extracts route args from context (same as sync version)
  • Injects Request object if handler declares one (same as sync version)
  • Calls the handler and detects if result is a coroutine
  • If coroutine: awaits it
  • Passes result through _to_response() (sync, CPU-bound — stays sync)
• Unit tests covering sync handler, async handler, and mixed scenarios
• Nothing calls it in the resolve chain yet — internal building block only

Alternative solutions

Acknowledgment

• This feature request meets Powertools for AWS Lambda (Python) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET