Fix farming performance windows

[nazar-pc]

Couple of things here:

• first of all, reads are a bit optimized: chunking of reads is now happening more accurately and efficiently
• second, unbuffered I/O is now also used for writes, looks like combining unbuffered reads with non-unbuffered writes triggers some bugs in Windows kernel: https://gist.github.com/nazar-pc/db418aeb3e23d6b6499d1ae9d4211290

Testing this in a VM for about an hour and some community testing will be happening here: https://forum.subspace.network/t/more-miss-reward-with-mar-11-release-in-windows/2948/48?u=nazar-pc

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