Add `no_std` support

`air-script` currently assumes `std` support, the goal is to make it `no_std` by default.

Original message by @bobbinth :
https://github.com/0xMiden/air-script/pull/376#discussion_r2071122538

Task list:
- [ ] default to `no_std`
- [ ] add `std` flag
- [ ] replace `std::collections` with appropriate `no_std` ones by default
- [ ] add tests, maybe comparing both outputs?

The issue is about modifying the crate to default to `no_std` and conditionally enable `std`. Start by examining the Cargo.toml and lib.rs for existing feature flags and `std` dependencies. Look for uses of `std::collections` to replace with `alloc` collections. The test strategy involves comparing outputs with and without the `std` feature.

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