proxy: Move binaries into the lib (#10758)

* This way all clippy lints defined in the lib also cover the binary
code.
* It's much easier to detect unused code.
* Fix all discovered lints.

proxy/src/binary/mod.rs

@@ -0,0 +1,7 @@
+//! All binaries have the body of their main() defined here, so that the code
+//! is also covered by code style configs in lib.rs and the unused-code check is
+//! more effective when practically all modules are private to the lib.
+
+pub mod local_proxy;
+pub mod pg_sni_router;
+pub mod proxy;