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, 9 insertions, 0 deletions

diff --git a/examples/example-metadata/Cargo.toml b/examples/example-metadata/Cargo.toml
new file mode 100644
index 0000000..eb34960
--- /dev/null
+++ b/examples/example-metadata/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "example-metadata"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+mingling = { path = "../../mingling" }
+
+[workspace]