* Only implement cache to MaskingExtent when off main thread
- It's possible for a [Chunk/Char]FilterBlock to be used multiple times in the same "tree" of method calls meaning the mutable paramets (particularly index) get increased within a loop, causing AIOOBs and other issues
- This is only possible on the main thread due to the handling of submissions in SingleThreadQueueExtent, as it ensures all operation remains on the main thread to prevent deadlocks
- Therefore safe usage of FilterBlocks requires that main-threaded operation create a new [Chunk/Char]FilterBlock instance each time
- Further fixes#1681
* Fix typos
* Switch to LongFunction
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