[multibyte] Implement interpreter semantics for array loads

[brendandahl]

Implement multibyte array load and store execution semantics in the interpreter.

This supports multi-element slicing across all numeric and vector array types, calculates effective addresses with static offsets, enforces total byte capacity bounds checks, and adds execution spec tests.

[brendandahl]

Some todos for further PRs:

• I think there's some work we could do to make this more efficient with template specialization for reading/writing fixed amounts of bytes.
• Add the remaining simd load, splat, lane instructions