[fix] Fix log for connection disconnected expectedly

[RobertIndie]

Fixes #140

Motivation

When running produce and consume, and the client calls close, it
shows ConnectError in the close method

[[127.0.0.1:43644](http://127.0.0.1:43644/) -> [127.0.0.1:6650](http://127.0.0.1:6650/)] Connection closed with
ConnectError

Modifications

• Show Connection disconnected just like the java client did instead of ConnectError when the client disconnect successfully.
• Add error log for unexpected closed connection.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

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