test_infra: Implement FromStr for GuestVmType

Add FromStr trait implementation for GuestVmType to enable
parsing from CLI string arguments. Supports "regular" and
"confidential" string values.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

test_infra/src/lib.rs

@@ -2493,6 +2493,18 @@ pub enum GuestVmType {
     Confidential,
 }
 
+impl FromStr for GuestVmType {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "regular" => Ok(GuestVmType::Regular),
+            "confidential" => Ok(GuestVmType::Confidential),
+            _ => Err(()),
+        }
+    }
+}
+
 // Get the direct igvm boot file path based on the console type
 fn direct_igvm_boot_path(console: Option<&str>) -> Option<PathBuf> {
     // get the default hvc0 igvm file if console string is not passed