runtime-rs: Remove direct implementation of ToString

Fix clippy error:
```
direct implementation of `ToString`
```
by switching to implement Display instead

Signed-off-by: stevenhorsman <steven@uk.ibm.com>

src/runtime-rs/crates/hypervisor/src/device/driver/vfio.rs

@@ -560,11 +560,8 @@ impl PCIeDevice for VfioDevice {
             ))?;
             hostdev.guest_pci_path = Some(pci_path.clone());
 
-            self.device_options.push(format!(
-                "0000:{}={}",
-                hostdev.bus_slot_func,
-                pci_path.to_string()
-            ));
+            self.device_options
+                .push(format!("0000:{}={}", hostdev.bus_slot_func, pci_path));
         }
 
         Ok(())

src/runtime-rs/crates/hypervisor/src/device/pci_path.rs

@@ -33,9 +33,9 @@ impl PciSlot {
     }
 }
 
-impl ToString for PciSlot {
-    fn to_string(&self) -> String {
-        format!("{:02x}", self.0)
+impl std::fmt::Display for PciSlot {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:02x}", self.0)
     }
 }
 
@@ -116,14 +116,17 @@ impl PciPath {
     }
 }
 
-impl ToString for PciPath {
-    // method to format the PciPath into a string
-    fn to_string(&self) -> String {
-        self.slots
-            .iter()
-            .map(|pci_slot| format!("{:02x}", pci_slot.0))
-            .collect::<Vec<String>>()
-            .join("/")
+impl std::fmt::Display for PciPath {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            self.slots
+                .iter()
+                .map(|pci_slot| format!("{:02x}", pci_slot.0))
+                .collect::<Vec<String>>()
+                .join("/")
+        )
     }
 }
 

src/runtime-rs/crates/hypervisor/src/qemu/cmdline_generator.rs

@@ -1540,13 +1540,14 @@ impl MonitorProtocol {
     }
 }
 
-impl ToString for MonitorProtocol {
-    fn to_string(&self) -> String {
-        match *self {
+impl std::fmt::Display for MonitorProtocol {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let to_string = match *self {
             MonitorProtocol::Hmp => "monitor".to_string(),
             MonitorProtocol::QmpPretty => "qmp-pretty".to_string(),
             _ => "qmp".to_string(),
-        }
+        };
+        write!(f, "{}", to_string)
     }
 }
 
@@ -1604,7 +1605,7 @@ impl QmpSocket {
 #[async_trait]
 impl ToQemuParams for QmpSocket {
     async fn qemu_params(&self) -> Result<Vec<String>> {
-        let param_qmp = format!("-{}", self.protocol.to_string());
+        let param_qmp = format!("-{}", self.protocol);
 
         let mut params: Vec<String> = Vec::new();
 

src/runtime-rs/crates/runtimes/common/src/types/mod.rs

@@ -78,9 +78,9 @@ pub struct ContainerID {
     pub container_id: String,
 }
 
-impl ToString for ContainerID {
-    fn to_string(&self) -> String {
-        self.container_id.clone()
+impl std::fmt::Display for ContainerID {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.container_id)
     }
 }