fix(core): classifier gaps for issue #201 builder split

Extract serve_pipeline from run.rs so all run* entrypoints share one
orchestration path. Add file-scope --lib run_with_shutdown tests that
mirror the pre-existing integration harness. Move extract tests to
tests/extract.rs and fix non-shutdown HTTP/3/dual-stack entrypoints so
on_shutdown hooks are not taken and dropped on pending delegates.

Author: Tuntii

crates/rustapi-core/src/app/mod.rs

@@ -7,6 +7,7 @@ mod openapi;
 mod production;
 mod routing;
 mod run;
+mod serve_pipeline;
 mod types;
 
 #[cfg(test)]