Be consistent when calculating sizes

[gekmihesg]

Ensure that passing the size as integer yields the same result as
passing the size as float.
Also support sizes below 1 KiB.

Before:

lvm::size_to_bytes(lvm::bytes_to_size(2047))   # 1024.0
lvm::size_to_bytes(lvm::bytes_to_size(2047.0)) # 2047.0
lvm::bytes_to_size(1023) # Evaluation Error: The value '' cannot be converted to Numeric.

After:

lvm::size_to_bytes(lvm::bytes_to_size(2047))   # 2047.0
lvm::size_to_bytes(lvm::bytes_to_size(2047.0)) # 2047.0
lvm::bytes_to_size(1023) # 1023.0b

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