refactor: improve redis client and publisher

- Refactor the redis client to use a mutex for thread safety.
- Improve error handling in context and playbook factory.
- Remove the play_mdbook command and associated tests.
- Add play_publisher command and tests for publishing books.
- Update the repository cache to use a reference to the redis client.

Co-authored-by: mahmmoud.hassanein <mahmmoud.hassanein@gmail.com>

lib/core/base/context.v

@@ -70,8 +70,8 @@ pub fn (mut self Context) redis() !&redisclient.Redis {
 			// make sure we are on the right db
 			r.selectdb(int(self.config.id))!
 		}
-		self.redis_ = &r
-		&r
+		self.redis_ = r
+		r
 	}
 
 	return r2