Send forget packet to avoid invisible chunk sections

[SirYwell]

Overview

Fixes #2989

Description

The vanilla 1.21.3 client handles full chunk packets in a way that previously empty chunk sections are not rendered. By forcing the client to drop the chunk completely first, we can ensure that the blocks are rendered again. This might cause some higher load for the client, so we should check if this is still a problem once 1.21.4 is released/supported.

Submitter Checklist

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[PierreSchwang]

sound reasonable - weird that that's a thing in 1.21.3 tbf