3. Arrays and tuples

Arrays are written as `T[]` or `Array<T>`. Every element must match the declared type, and the compiler checks methods like `.push()` and `.map()` accordingly.

Tuples are fixed-length arrays where each position has its own type — perfect for things like `[address, amount]` pairs.

Tuples can also have named elements and optional/rest positions, e.g. `[to: string, amount: number, memo?: string]`, which documents intent while keeping the same underlying array shape.