A lot of strings and arrays used in nftables structures are static, but
currently we need to do allocations everywhere using owned String and Vec.
Replace them with Cow so we can pass &'static str or &'static [_] whenever
possible, while returning owned value when deserializing.

This evens out some of the large enums' sizes (e.g. Expression and Statement's)
from over 200 bytes to <=144. Further reduction could be done, as this commit
only changes the obvious ones for now.

Also moves BinaryOperation's Box up one level so it only uses one Box.

Since we only expect two elements from Range, we can just use array instead.

This fails to build on 1.65:

```
error[E0277]: the trait bound `[SetItem]: ToOwned` is not satisfied in `Expression`
   --> src/stmt.rs:245:14
    |
245 |     pub dev: Option<Expression>,
    |              ^^^^^^^^^^^^^^^^^^ within `Expression`, the trait `ToOwned` is not implemented for `[SetItem]`, which is required by `Expression: Sized`
    |
    = help: the trait `ToOwned` is implemented for `[T]`
note: required because it appears within the type `Expression`
   --> src/expr.rs:10:10
    |
10  | pub enum Expression {
    |          ^^^^^^^^^^
note: required by an implicit `Sized` bound in `std::option::Option`
   --> /rustc/9b00956e56009bab2aa15d7bff10916599e3d6d6/library/core/src/option.rs:572:1

...and many, many similar errors
```

It compiles successfully on Rust >=1.79, so this commit can be reverted once our MSRV reaches it.

This adds a bunch of lifetimes, but it works with `.into()` when a borrowed value's array container is stored in another place, without the need of `Cow::Borrowed`:

```
let objects = [
    NfObject::ListObject(NfListObject::Table(Table {
        family: NfFamily::INet,
        name: "some_inet_table".into(), // here
        handle: None,
    })),
    // ...
];
let expected = Nftables {
    objects: objects.into(); // and here
};
```

However, `Cow::{Borrowed, Owned}` still needs to be used when you want to write the above in one statement.