nested slices break the parser and some Middle IR assumptions

Currently, nesting slices breaks the parser: `arr[0..5][2..4]`. Introducing indirection with a let statement or function calls is not expressible in the current MIR.

The current way to bypass this issue is to use nested evaluator calls:
```air-script
trace_columns {
main: [a[10]],
}
integrity_constraints {
enf f(a[0..5]);
}
ev f([a[5]) {
enf g([a[2..5]);
}
ev g([a[3]) {
enf x^2 = x for x in a;
}
```

The behaviour should replicate what is done for evaluator calls in #495, likely by fixing the parser and by enabling support for `MirAccessType::Slice` in MIR.

The issue is about nested slices in the parser and MIR (Middle IR). Start by examining the parser code for handling slice expressions like `arr[0..5][2..4]` and the MIR representation for `MirAccessType::Slice`. Look at how issue #495 handled evaluator calls as a reference. The fix likely involves modifying the grammar and updating MIR to support nested slice accesses. Test changes with the provided air-script example to ensure nested slices are parsed and lowered correctly.

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