use bit32 in base85.decode -> speed

[idontyboi]

Hello, what you use on base85.decode looks like using math.floor to extract bits from numbers. You can use bit32.extract instead to gain some speedup (and bit32.rshift for the first byte)

BEFORE: 2.691, 2.701, 2.694, 2.706, 2.708 AFTER: 2.444, 2.436, 2.440, 2.446, 2.438

total speedup: 10.5%

Can't sumbit a PR or patch due to Public Domain requirements, though.