Improve performance of chunk loaded metric and offline player count

[radiant-ai]

Noticed spike of mspt on regular interval and upon inspection noticed that the main contributor are three metrics of the plugin:

For players total metric. Solution:

• make the collection async, it looks like server only reads players from .dat files to do it, which is safe to run off the main thread

For loaded chunks count. It looks like the getLoadedChunks() method makes a copy of all the chunks, which is extremely slow when there are many chunks loaded. Solution:

• do the call only once when the metric is first requested, calculate all subsequent metrics by manually tracking number of loaded chunks per word.

Regarding entities, it is also possible to do same approach as with chunks, but this will be a bit more effort.

[sladkoff]

Hi @radiant-ai can you please rebase? The CI build has been fixed on master.

[sladkoff]

@radiant-ai Thank you 🙏