Prep to release v0.42.0 (#2003)

* Prep to release v0.42.0

* Remove test_context reference from example

* standalone_crate for doc tests because codegen is expensive

* fmt

codegen/src/api/constants.rs

@@ -14,7 +14,7 @@ use super::CodegenError;
 /// Generate constants from the provided pallet's metadata.
 ///
 /// The function creates a new module named `constants` under the pallet's module.
-/// ```ignore
+/// ```rust,ignore
 /// pub mod PalletName {
 ///     pub mod constants {
 ///     ...

codegen/src/api/events.rs

@@ -13,7 +13,7 @@ use subxt_metadata::PalletMetadata;
 ///
 /// The function creates a new module named `events` under the pallet's module.
 ///
-/// ```ignore
+/// ```rust,ignore
 /// pub mod PalletName {
 ///     pub mod events {
 ///     ...
@@ -24,7 +24,7 @@ use subxt_metadata::PalletMetadata;
 /// The function generates the events as rust structs that implement the `subxt::event::StaticEvent` trait
 /// to uniquely identify the event's identity when creating the extrinsic.
 ///
-/// ```ignore
+/// ```rust,ignore
 /// pub struct EventName {
 ///      pub event_param: type,
 /// }

codegen/src/api/mod.rs

@@ -410,19 +410,24 @@ pub struct StructFromVariant {
 /// Returns the TokenStream of the type alias module.
 ///
 /// E.g a struct like this:
-/// ```ignore
+///
+/// ```rust,ignore
 /// pub struct SetMaxCodeSize {
 ///     pub new: ::core::primitive::u32,
 /// }
 /// ```
+///
 /// will be made into this:
-/// ```ignore
+///
+/// ```rust,ignore
 /// pub struct SetMaxCodeSize {
 ///     pub new: set_max_code_size::New,
 /// }
 /// ```
+///
 /// And the type alias module will look like this:
-/// ```ignore
+///
+/// ```rust,ignore
 /// pub mod set_max_code_size {
 ///     use super::runtime_types;
 ///     pub type New = ::core::primitive::u32;

codegen/src/lib.rs

@@ -40,7 +40,7 @@ pub use syn;
 ///
 /// Generating an interface using all of the defaults:
 ///
-/// ```rust
+/// ```rust,standalone_crate
 /// use codec::Decode;
 /// use subxt_codegen::{ Metadata, CodegenBuilder };
 ///