Fix arrays to store their primitive elements contiguously.

[otrho]

At the moment all types smaller than 64 bits are cast up to 64 bit values in the ASM generation, so they fit in a register nicely, and work easily with lw and sw. This is also true for arrays, so an array of bytes is actually converted to an array of u64. This is both wasteful and unexpected, from a developer point of view.

[otrho]

Having [byte] actually mean a stream of bytes would already be useful for the B512 type in the Sway std library.

[adlerjohn]

Something to consider: the internal memory representation is currently identical to the ABI representation. This allows no-copy, direct use of parameters passed in from userspace (with an optional safety check that's either constant-time or linear in the number of fields rather than linear in the number of bytes, as a serialize/deserialize pass would be).

Changing anything about the internal representation of things also requires a change to the ABI specification to preserve this property.

[otrho]

This talks specifically about padding smaller values. https://github.com/FuelLabs/fuel-specs/blob/master/specs/protocol/abi.md#unsigned-integers

And here for arrays https://github.com/FuelLabs/fuel-specs/blob/master/specs/protocol/abi.md#array