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, 10 insertions, 0 deletions

diff --git a/examples/example-combine-pathf-metadata/page.toml b/examples/example-combine-pathf-metadata/page.toml
new file mode 100644
index 0000000..76c1700
--- /dev/null
+++ b/examples/example-combine-pathf-metadata/page.toml
@@ -0,0 +1,10 @@
+[example]
+id = "example-combine-pathf-metadata"
+name = "Pathfinder + Metadata"
+icon = "🧭"
+category = "advanced"
+desc = """
+Combines the `pathf` feature with entry metadata. The metadata `DataType` and the entry `BindType` are defined inside a submodule, and `pathf` resolves them for `gen_program!()` at build time.
+"""
+tags = ["pathf", "metadata", "build.rs"]
+files = ["src/main.rs", "src/sub/mod.rs", "build.rs", "Cargo.toml"]