[ty] Shrink size of AstNodeRef (#20028)

## Summary

Removes the `module_ptr` field from `AstNodeRef` in release mode, and
change `NodeIndex` to a `NonZeroU32` to reduce the size of
`Option<AstNodeRef<_>>` fields.

I believe CI runs in debug mode, so this won't show up in the memory
report, but this reduces memory by ~2% in release mode.

crates/ruff_python_parser/src/lib.rs

@@ -215,7 +215,7 @@ pub fn parse_parenthesized_expression_range(
 ///     value: "'''\n int | str'''".to_string().into_boxed_str(),
 ///     flags: StringLiteralFlags::empty(),
 ///     range: TextRange::new(TextSize::new(0), TextSize::new(16)),
-///     node_index: AtomicNodeIndex::dummy()
+///     node_index: AtomicNodeIndex::NONE
 /// };
 /// let parsed = parse_string_annotation("'''\n int | str'''", &string);
 /// assert!(!parsed.is_ok());