docs: fix doctest compilation errors in actor.rs and gen_server.rs

- Fix string comparison in actor.rs try_receive example by using s.as_str()
  to properly compare &String with string literal
- Add missing CallResponse import in gen_server.rs module doctest example
- All 81 unit tests, integration tests, and 85 doctests now passing

Author: am-kantox

joerl/src/actor.rs

@@ -429,7 +429,7 @@ impl ActorContext {
     ///         // Check if there's a ready message without waiting
     ///         if let Some(ready) = ctx.try_receive(|msg| {
     ///             msg.downcast_ref::<String>()
-    ///                 .filter(|s| s == "ready")
+    ///                 .filter(|s| s.as_str() == "ready")
     ///                 .cloned()
     ///         }) {
     ///             println!("Got ready signal: {}", ready);

joerl/src/gen_server.rs

@@ -26,7 +26,7 @@
 //! In joerl, the equivalent looks like:
 //!
 //! ```rust
-//! use joerl::gen_server::{GenServer, GenServerContext};
+//! use joerl::gen_server::{GenServer, GenServerContext, CallResponse};
 //! use async_trait::async_trait;
 //!
 //! struct Counter;