Narrow integer instructions

[Dentosal]

Closes #626. VM PRs: FuelLabs/fuel-vm#922 and FuelLabs/fuel-vm#923.

Implementing correct overflow handling for narrow integer types (u8, u16, u32) is tedious, error prone, and needs lots of instructions. Likewise, memory load/store operations with these involve lots of expensive bitmasking. This change provides the functionality on the vm level.

Only operations for which the overflow handling is different with narrow integers are implemented. For instance, multiplication is definitely different as 256 * 2 overflows u8 but doesn't overflow u64. In comparison, division is not, it never creates results larger than the original value.

The operations silently truncate the input operands to the correct bit width, meaning that niop $ra $rb $rc NIOP_U8 | NIOP_ADD with $rb = 0xff01, $rc = 0x02 sets $ra = 3 without panicking. Same goes for store operations, and that was already the case with SB. It's up to the compiler or user to take this into account.

As always I'm trying to sneak in cool new features. Here it's the XNOR operating mode, which is extremely useful for generating bitmasks. For instance niop $ra $zero $zero NIOP_U32 | NIOP_XNOR sets $ra to 0xffffffff.

Before requesting review

• I have reviewed the code myself

After merging, notify other teams

• Sway compiler
• Platform documentation (for out-of-organization contributors, the person merging the PR will do this)