Allow bus operations to be defined without a selector

Currently, bus operations require a selector / multiplicity set with the `when` / `for` keywords:

```
p.remove(3, 4) when s;
q.insert(3, 4) for 2;
```

The following statement is not valid:
```
p.remove(3, 4);
```

It could be useful to allow this kind of statements, to use them in match statements, for instance:

```
ev evaluator_with_bus([a, b, c]) {
[...]
p.remove(3, 4);
}

match {
case s2: enf evaluator_with_bus([a, b, c]),
[...]
}
```

In this case, the match statement for this bus would be equivalent to:
```
p.remove(3, 4) when s2;
```

The use case for this
_Originally posted by @bobbinth in https://github.com/0xMiden/air-script/pull/413#discussion_r2234955653_

The issue is about the language grammar and parser for bus operations in air-script. Look at the parser code (likely in a `parser/` or `src/` directory) for handling bus operation statements like `p.remove(3, 4) when s;`. The change involves allowing statements without the `when` or `for` clause. Check the AST definition and the match statement handling. A good starting point is the linked PR #413 discussion. Verify the change by writing a test case for the new syntax.

Escrita pelo modelo de indexação a partir do texto da issue.