feat: add entry metadata system with compile-time typed values

Add `Metadata<B>` trait and `#[metadata(Entry)]` attribute macro
to attach arbitrary, compile-time-typed metadata to entries.
Implement `ProgramCollect::get_metadata<T>()` for runtime retrieval,
backed by a global registry populated by `register_metadata!`.

Extend `pathf` with `MetadataPattern` to resolve metadata types
across modules at build time. Add two examples demonstrating
metadata usage with and without pathf integration.

1 files changed, 35 insertions, 0 deletions

diff --git a/examples/test-examples.toml b/examples/test-examples.toml
index b74c9a5..03df5e1 100644
--- a/examples/test-examples.toml
+++ b/examples/test-examples.toml
@@ -327,3 +327,38 @@ expect.result = "Hello, Alice"
 command = "goodbye"
 expect.exit-code = 0
 expect.result = "Goodbye!"
+
+[[test.example-metadata]]
+command = "greet"
+expect.exit-code = 0
+expect.result = "Hello, World!"
+
+[[test.example-metadata]]
+command = "greet Alice"
+expect.exit-code = 0
+expect.result = "Hello, Alice!"
+
+[[test.example-metadata]]
+command = "desc"
+expect.exit-code = 0
+expect.result = "EntryGreet desc = ok"
+
+[[test.example-metadata]]
+command = "nodoc"
+expect.exit-code = 0
+expect.result = "EntryDescription has no description"
+
+[[test.example-combine-pathf-metadata]]
+command = "hello"
+expect.exit-code = 0
+expect.result = "Hello, World!"
+
+[[test.example-combine-pathf-metadata]]
+command = "hello Alice"
+expect.exit-code = 0
+expect.result = "Hello, Alice!"
+
+[[test.example-combine-pathf-metadata]]
+command = "desc"
+expect.exit-code = 0
+expect.result = "EntryHello desc = okay"