[main] Add must_use attributes to methods returning Self (Azure#6268)

Satisfy clippy.

## Azure IoT Edge PR checklist:

mqtt/edgelet-client/src/workload/client.rs

@@ -74,7 +74,7 @@ impl WorkloadClient {
         let uri =
             make_hyper_uri(&self.scheme, &path).map_err(|e| ApiError::ConstructRequestUrl(e))?;
 
-        let req = SignRequest::new(base64::encode(data.to_string()));
+        let req = SignRequest::new(base64::encode(data));
         self.post(uri, req, StatusCode::OK).await
     }
 

mqtt/edgelet-client/src/workload/models/cert_response.rs

@@ -26,6 +26,7 @@ impl CertificateResponse {
         self.private_key = private_key;
     }
 
+    #[must_use]
     pub fn with_private_key(mut self, private_key: PrivateKey) -> Self {
         self.private_key = private_key;
         self
@@ -39,6 +40,7 @@ impl CertificateResponse {
         self.certificate = certificate;
     }
 
+    #[must_use]
     pub fn with_certificate(mut self, certificate: String) -> Self {
         self.certificate = certificate;
         self
@@ -52,6 +54,7 @@ impl CertificateResponse {
         self.expiration = expiration;
     }
 
+    #[must_use]
     pub fn with_expiration(mut self, expiration: String) -> Self {
         self.expiration = expiration;
         self
@@ -90,6 +93,7 @@ impl PrivateKey {
         self.type_ = type_;
     }
 
+    #[must_use]
     pub fn with_type(mut self, type_: String) -> Self {
         self.type_ = type_;
         self
@@ -103,6 +107,7 @@ impl PrivateKey {
         self.ref_ = Some(ref_);
     }
 
+    #[must_use]
     pub fn with_ref(mut self, ref_: String) -> Self {
         self.ref_ = Some(ref_);
         self
@@ -120,6 +125,7 @@ impl PrivateKey {
         self.bytes = Some(bytes);
     }
 
+    #[must_use]
     pub fn with_bytes(mut self, bytes: String) -> Self {
         self.bytes = Some(bytes);
         self

mqtt/edgelet-client/src/workload/models/identity_cert.rs

@@ -8,15 +8,16 @@ pub struct IdentityCertificateRequest {
 }
 
 impl IdentityCertificateRequest {
-    pub fn new(expiration: Option<String>) -> IdentityCertificateRequest {
+    pub fn new(expiration: Option<String>) -> Self {
         IdentityCertificateRequest { expiration }
     }
 
     pub fn set_expiration(&mut self, expiration: String) {
         self.expiration = Some(expiration);
     }
 
-    pub fn with_expiration(mut self, expiration: String) -> IdentityCertificateRequest {
+    #[must_use]
+    pub fn with_expiration(mut self, expiration: String) -> Self {
         self.expiration = Some(expiration);
         self
     }

mqtt/edgelet-client/src/workload/models/server_cert.rs

@@ -23,6 +23,7 @@ impl ServerCertificateRequest {
         self.common_name = common_name;
     }
 
+    #[must_use]
     pub fn with_common_name(mut self, common_name: String) -> Self {
         self.common_name = common_name;
         self
@@ -36,6 +37,7 @@ impl ServerCertificateRequest {
         self.expiration = expiration;
     }
 
+    #[must_use]
     pub fn with_expiration(mut self, expiration: String) -> Self {
         self.expiration = expiration;
         self

mqtt/edgelet-client/src/workload/models/sign_request.rs

@@ -28,6 +28,7 @@ impl SignRequest {
         self.key_id = key_id;
     }
 
+    #[must_use]
     pub fn with_key_id(mut self, key_id: String) -> Self {
         self.key_id = key_id;
         self
@@ -41,6 +42,7 @@ impl SignRequest {
         self.algorithm = algorithm;
     }
 
+    #[must_use]
     pub fn with_algorithm(mut self, algorithm: Algorithm) -> Self {
         self.algorithm = algorithm;
         self
@@ -54,6 +56,7 @@ impl SignRequest {
         self.data = data;
     }
 
+    #[must_use]
     pub fn with_data(mut self, data: String) -> Self {
         self.data = data;
         self
@@ -86,6 +89,7 @@ impl SignResponse {
         self.digest = digest;
     }
 
+    #[must_use]
     pub fn with_digest(mut self, digest: String) -> Self {
         self.digest = digest;
         self

mqtt/edgelet-client/src/workload/models/trust_bundle.rs

@@ -16,6 +16,7 @@ impl TrustBundleResponse {
         self.certificate = certificate;
     }
 
+    #[must_use]
     pub fn with_certificate(mut self, certificate: String) -> Self {
         self.certificate = certificate;
         self

mqtt/mqtt-bridge/src/pump/builder.rs

@@ -56,6 +56,7 @@ where
     S: StreamWakeableState + Send,
 {
     /// Apples parameters to create local pump.
+    #[must_use]
     pub fn with_local<F>(mut self, mut apply: F) -> Self
     where
         F: FnMut(&mut PumpBuilder),
@@ -65,6 +66,7 @@ where
     }
 
     /// Applies parameters to create remote pump.
+    #[must_use]
     pub fn with_remote<F>(mut self, mut apply: F) -> Self
     where
         F: FnMut(&mut PumpBuilder),

mqtt/mqtt-broker-tests-util/src/client.rs

@@ -167,26 +167,31 @@ where
         }
     }
 
+    #[must_use]
     pub fn with_client_id(mut self, client_id: ClientId) -> Self {
         self.client_id = client_id;
         self
     }
 
+    #[must_use]
     pub fn with_username(mut self, username: &str) -> Self {
         self.username = Some(username.into());
         self
     }
 
+    #[must_use]
     pub fn with_password(mut self, password: &str) -> Self {
         self.password = Some(password.into());
         self
     }
 
+    #[must_use]
     pub fn with_will(mut self, will: Publication) -> Self {
         self.will = Some(will);
         self
     }
 
+    #[must_use]
     pub fn with_keep_alive(mut self, keep_alive: Duration) -> Self {
         self.keep_alive = keep_alive;
         self

mqtt/mqtt-broker/src/broker.rs

@@ -1063,11 +1063,13 @@ where
         }
     }
 
+    #[must_use]
     pub fn with_state(mut self, state: BrokerSnapshot) -> Self {
         self.state = Some(state);
         self
     }
 
+    #[must_use]
     pub fn with_config(mut self, config: BrokerConfig) -> Self {
         self.config = config;
         self

mqtt/mqtt-broker/src/persist.rs

@@ -104,6 +104,7 @@ impl<F> FilePersistor<F> {
     /// The intent is to allow rollback to a pervious state.
     /// The default is `2`, which saves the current and previous state.
     /// The minimum value is `1` (the current state).
+    #[must_use]
     pub fn with_previous_count(mut self, previous_count: usize) -> Self {
         self.previous_count = cmp::max(1, previous_count);
         self

mqtt/policy/src/core/builder.rs

@@ -101,6 +101,7 @@ where
 
     /// Specifies the default decision that `Policy` will return if
     /// no rules match the request.
+    #[must_use]
     pub fn with_default_decision(mut self, decision: Decision) -> Self {
         self.default_decision = decision;
         self