Background

When the metrics feature is enabled, define_metrics! registers each metrics type’s init via a ctor before main.

The current code uses ctor(anonymous, …). Using anonymous tends to produce the same linker-visible symbol for every macro expansion. With multiple crates or multiple define_metrics! expansions, this can cause symbol collisions or only one ctor surviving linkage, leading to partial registration or order-dependent behavior that is hard to debug.

Expected behavior

Each define_metrics! expansion should get a struct-distinct ctor registration symbol instead of sharing anonymous.

Suggested approach

• Drop anonymous from the ctor, keeping only the required crate_path (to $crate::__private_ctor).
• Name the ctor callback function after the metrics struct ($name()); types and functions live in different namespaces, so $name::init remains valid.
• Apply #[allow(non_snake_case)] on the generated function to silence lint for PascalCase function names.