Add word alignment checks for LOAD32 and STORE32

[thealmarty]

If any of the read/write addresses are not multiple of 4, the VM panics with an error message describing which opcode and read/write address is the problem.

I've confirmed that these checks work on runtime. I.e., I made a false assertion to an address value and confirmed that the VM does panic.

I've confirmed that cargo test and C unit tests all pass locally.

[thealmarty]

Sorry I'm having second thoughts on this. Perhaps this is overkill and I should use debug_assert instead? I'm worried about affecting the performance with assert. If the words are not aligned, the prover should fail to prove, and then users can check with our debug version of the VM?

[morganthomas]

I don't think execution costs are much of a concern at this point because proving costs are so much higher. I'm fine with it as is.