write MidenVM constraints for system (clk constraint)

Most of the system constraints depend on the stack and are therefore more challenging and should be done separately, but the `clk` constraint can be done first. It's implemented in Rust [here](https://github.com/0xPolygonMiden/miden-vm/blob/main/air/src/lib.rs).

It's possible that this constraint is not documented in the Miden VM design docs - I didn't find it. It would be good to double-check this and also update the MidenVM docs to correct this.

- [ ] add `clk` constraint
- [ ] search the MidenVM design docs for the `clk` constraint and update the docs if not found

The issue points to the Rust implementation in the miden-vm repository's air/src/lib.rs. First, examine that file to understand the existing clk constraint. Then, search the Miden VM design docs for any mention of the clk constraint. The task involves implementing the constraint in Air-Script and potentially updating the documentation. A newcomer would need to understand AIR constraints and the Miden VM architecture.

Scritto dal modello di indicizzazione a partire dal testo della issue.