refactor!: replace pack! macros with derive-based pipeline types

Remove the `pack!`, `pack_err!`, `pack_structural!`, and
`pack_err_structural!` macros, replacing all pipeline type definitions
with `#[derive(Grouped)]` and `#[derive(Grouped, Wrap)]` attributes.
This changes the generated struct shape from named-field structs with an
`inner` field to tuple structs accessed via `.0`, and removes the
auto-generated `name` and `info` fields from error types.

1 files changed, 8 insertions, 5 deletions

diff --git a/examples/example-metadata/src/main.rs b/examples/example-metadata/src/main.rs
index 94facb4..99a8aae 100644
--- a/examples/example-metadata/src/main.rs
+++ b/examples/example-metadata/src/main.rs
@@ -56,14 +56,17 @@ pub fn greet_desc() -> Description {
 }
 // --------- IMPORTANT ---------
 
-pack!(ResultName = String);
-pack!(DescResult = String);
+#[derive(Grouped, Wrap)]
+pub struct ResultName(String);
+
+#[derive(Grouped, Wrap)]
+pub struct DescResult(String);
 
 /// Chain for `greet` — reads the name and produces a `ResultName`.
 #[chain]
 fn handle_greet(args: EntryGreet) -> Next {
     let name: ResultName = args
-        .inner
+        .0
         .first()
         .cloned()
         .unwrap_or_else(|| "World".to_string())
@@ -81,7 +84,7 @@ fn handle_desc(_args: EntryDescription) -> Next {
         None => "EntryGreet has no description".to_string(),
     };
     // --------- IMPORTANT ---------
-    DescResult::new(msg).to_render()
+    DescResult(msg).to_render()
 }
 
 /// Chain for `nodoc` — asks for metadata on an entry that has none.
@@ -94,7 +97,7 @@ fn handle_nodoc(_args: EntryNoDescription) -> Next {
         None => "EntryDescription has no description".to_string(),
     };
     // --------- IMPORTANT ---------
-    DescResult::new(msg).to_render()
+    DescResult(msg).to_render()
 }
 
 /// Renders the greeting message with the provided name.