Investigate potential WASIX breakage due to Rust 1.77 u128 alignment changes

[theduke]

Rust 1.77 will change the alignment of i/u128 to 16 bytes on x86.

We use u128 in exactly one place in WASIX, namely in the StackSnapshot.
This may cause breakage due to alignment shifts in the struct.

We need to investigate if this will break anything.

[syrusakbary]

One possible solution: use two u64 to represent it