Make SpanId and RegId also use new ID struct (#13963)

# Description
In the PR #13832 I used some newtypes for the old IDs. `SpanId` and
`RegId` already used newtypes, to streamline the code, I made them into
the same style as the other marker-based IDs.

Since `RegId` should be a bit smaller (it uses a `u32` instead of
`usize`) according to @devyn, I made the `Id` type generic with `usize`
as the default inner value.

The question still stands how `Display` should be implemented if even.

# User-Facing Changes
Users of the internal values of `RegId` or `SpanId` have breaking
changes but who outside nushell itself even uses these?

# After Submitting
The IDs will be streamlined and all type-safe.

crates/nu-protocol/src/ast/expression.rs

@@ -584,7 +584,7 @@ impl Expression {
         Expression {
             expr,
             span,
-            span_id: SpanId(0),
+            span_id: SpanId::new(0),
             ty,
             custom_completion: None,
         }