Codegen for custom values in metadata (#1117)

* work in progress

* add custom types access

* nit

* custom values client

* adjust light client

* adjust doc comments

* adjust book for custom values in code gen

* format and check docs

* work in progress

* add custom types access

* nit

* custom values client

* adjust light client

* codegen and validation

* adjust docs

* use ignore in docs in book

* change iter implementation

* use validation hash and other codegen changes

* add ui test for custom values codegen

* allow 'latest' metadata to be returned from the fallback code (#1127)

* nits

* fix validation check

* fix comments

* nits

---------

Co-authored-by: James Wilson <james@jsdw.me>

metadata/src/utils/variant_index.rs

@@ -21,7 +21,7 @@ impl VariantIndex {
     /// Build indexes from the optional variant ID.
     pub fn build(variant_id: Option<u32>, types: &PortableRegistry) -> Self {
         let Some(variants) = Self::get(variant_id, types) else {
-            return Self::empty()
+            return Self::empty();
         };
 
         let mut by_name = HashMap::new();
@@ -47,11 +47,9 @@ impl VariantIndex {
         variant_id: Option<u32>,
         types: &PortableRegistry,
     ) -> Option<&[Variant<PortableForm>]> {
-        let Some(variant_id) = variant_id else {
-            return None
-        };
+        let variant_id = variant_id?;
         let TypeDef::Variant(v) = &types.resolve(variant_id)?.type_def else {
-            return None
+            return None;
         };
         Some(&v.variants)
     }