Complete ResponseCallbackWrapper on encoding failure

[Denovo1998]

https://github.com/Denovo1998/starlight-for-kafka/actions/runs/20877709389?pr=1

Motivation

ResponseCallbackWrapper is used to run cleanup logic after a response is written to the network channel. When KafkaCommandDecoder fails to convert a response to ByteBuf, we currently send an error response but never invoke the wrapper’s completion callback, which can leave cleanup logic unexecuted and potentially leak in-flight request state. This PR ensures the callback is completed on the failure path as well, and aligns the related fetch test to always complete the wrapper after inspection.

Modifications

• Call ResponseCallbackWrapper#responseComplete() when responseToByteBuf throws, before sending an error response.
• Update KafkaApisTest#testFetchMinBytesSingleConsumer to always invoke responseComplete() in a finally block after asserting on the wrapped response.