chore(release): v0.5.0

Breaking API rename since v0.4.0: gen_server's ServerRef/ServerBuilder/
ServerCtx -> GenServerRef/GenServerBuilder/GenServerCtx, Watcher<G> is
now generic over its GenServer, and GenServer gained a required
associated Timer type for timer-fire payloads (arm_after/handle_timer).
Downstream consumers (urus) have been ported.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "smarm"
-version = "0.4.0"
+version = "0.5.0"
 edition = "2021"
 rust-version = "1.95"