fix(kds): remove context from map on stream close

[lukidzi]

Motivation

The application's memory usage was slowly increasing but did not correlate with the number of active connections. I decided to investigate the memory usage and noticed some context entries. While reviewing the code, I discovered that we are not cleaning up the map of streams and contexts. I'm not certain if this is the primary issue, but it could be a contributing factor.

Implementation information

Implemented the OnDeltaStreamClosed method to remove entries from the map when a stream is closed.

Supporting documentation

xref: https://github.com/Kong/kong-mesh/issues/6616

[github-actions]

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[slonka]

Nice catch!