Replace raw usize IDs with new types (#13832)

# Description

In this PR I replaced most of the raw usize IDs with
[newtypes](https://doc.rust-lang.org/rust-by-example/generics/new_types.html).
Some other IDs already started using new types and in this PR I did not
want to touch them. To make the implementation less repetitive, I made
use of a generic `Id<T>` with marker structs. If this lands I would try
to move make other IDs also in this pattern.

Also at some places I needed to use `cast`, I'm not sure if the type was
incorrect and therefore casting not needed or if actually different ID
types intermingle sometimes.

# User-Facing Changes

Probably few, if you got a `DeclId` via a function and placed it later
again it will still work.

crates/nu-plugin-core/src/util/with_custom_values_in.rs

@@ -1,5 +1,8 @@
 use nu_protocol::{CustomValue, IntoSpanned, ShellError, Spanned, Value};
 
+#[allow(unused_imports)] // both are definitely used
+use nu_protocol::{BlockId, VarId};
+
 /// Do something with all [`CustomValue`]s recursively within a `Value`. This is not limited to
 /// plugin custom values.
 pub fn with_custom_values_in<E>(
@@ -36,8 +39,8 @@ fn find_custom_values() {
         ]),
         "closure" => Value::test_closure(
             Closure {
-                block_id: 0,
-                captures: vec![(0, cv.clone()), (1, Value::test_string("foo"))]
+                block_id: BlockId::new(0),
+                captures: vec![(VarId::new(0), cv.clone()), (VarId::new(1), Value::test_string("foo"))]
             }
         ),
     });