Ensure that scripts, predicates, and byte code len % 4 == 0

[MitchTurner]

Replacing FuelLabs/fuel-tx#150

Currently the behavior in the code doesn't match the behavior in specs. We can also optionally rephrase the specs to be "% 4", but that isn't necessary.

[Voxelot]

This isn't necessarily a hard requirement, for example some sway programs have arbitrary data blobs like constants at the end of the bytecode. So we shouldn't assume all bytecode is divisible into executable instructions.

[xgreenx]

Then we need to update specification to remove scriptLength * 4 = len(script)

[MukulKolpe]

Hey @xgreenx can I work on this one?