Exception in application code does not clear the idempotency key

[shalabhc]

The idempotency key is cleared when a response flows through the send_wrapper here:

asgi-idempotency-header/idempotency_header_middleware/middleware.py

Line 75 in 8f89a5c

await self.backend.clear_idempotency_key(idempotency_key)

and here:

asgi-idempotency-header/idempotency_header_middleware/middleware.py

Line 83 in 8f89a5c

await self.backend.clear_idempotency_key(idempotency_key)

However if the underlying application raises an exception, it does not flow through the send_wrapper so the key is not cleared. The self.app() call can be wrapped in a try/finally to handle that case:

asgi-idempotency-header/idempotency_header_middleware/middleware.py

Line 95 in 8f89a5c

await self.app(scope, receive, send_wrapper)

If there is an exception converted to a 500 or another response by an outer middleware, the idempotency key for that request will not be cleared.

Wrapping the app() in a middleware is a common pattern, eg:

https://github.com/steinnes/timing-asgi/blob/2a0dd6535b740481f4354831a37b92b47a70d4c2/timing_asgi/middleware.py#L70
https://github.com/DataDog/dd-trace-py/blob/6d98a05ff80b572b265fac3562e207f17c2d9adb/ddtrace/contrib/asgi/middleware.py#L291

The change is simple but I am unable to set up a working test environment so I wasn't able to write a test.