Pick a better memory size for uncompress

[fnands]

When uncompressing, we need to allocate some memory for the uncompressed data.
Currently this is done as:

mimage/mimage/utils/compression.mojo

Line 43 in 3805a6a

var data_memory_amount: Int = len(data) * 100

This is dumb. It should be possible to calculate the size needed from the image metadata.