Ability to send block changes from chunks not in view

Currently when a `sendBlockChange` or a `send#Change` method in GlowPlayer is called, action will only occur if the chunk is visible to the client at that current time.

It would be nice if you could send a block change in a chunk the client doesn't know about, for it to optionally be stored in memory and when their known chunks update, for it to send the block change if it belongs to that chunk.

I could work on this when I have free time if this is an approved idea.

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Start by locating GlowPlayer and its sendBlockChange/send#Change methods, then trace how visible or known chunks are determined and updated. The issue is complete when an optionally retained block change for an unknown chunk is sent once that chunk becomes known; no file or test is named, so the relevant coverage will need to be found.

Written by the indexing model from the issue text.