Safety: Bit sizes and overflows

# Why?

Lean has big arithmetics, WASM, obviously, not.

# How

- [ ] Before constructing an Int or anything else, check bit size of the constructed object
- [ ] Same applies when we create a new object as a result of an operation on some objects

The issue names no files, tests, or entry points. Start by locating where Int values and operation results are constructed, then determine the WebAssembly bit-size limits that must be enforced. Done means oversized constructions and arithmetic results are checked consistently, with tests covering overflow cases.

Written by the indexing model from the issue text.