Returns the length of a raw slice.
The returned value is the number of **elements**, not the number of bytes.
This function is safe, even when the raw slice cannot be cast to a slice
reference because the pointer is null or unaligned.
# Original
- [`<*[T]>::len`][orig]
- [`NonNull::len`]
# Similar Functions
- [`Pointer::len`]
- [`NonNullPointer::len`]
# Examples
```rust
use pointdexter::prelude::*;
let slice = ptxr::null::<i8, Shared>().make_slice(3);
assert_eq!(slice.len(), 3);
let slice = NonNullPointer::<i8, Shared>::dangling().make_slice(3);
assert_eq!(slice.len(), 3);
```
[orig]: https://doc.rust-lang.org/std/primitive.pointer.html#method.len