fix: building of W3C credential values passed through the FFI (#323)

Signed-off-by: artem.ivanov <artem.ivanov@dsr-corporation.com>

src/services/w3c/types.rs

@@ -6,9 +6,14 @@ pub struct MakeCredentialAttributes(pub(crate) CredentialSubject);
 
 impl MakeCredentialAttributes {
     pub fn add(&mut self, name: impl Into<String>, raw: impl Into<String>) {
-        self.0
-             .0
-            .insert(name.into(), CredentialAttributeValue::String(raw.into()));
+        let string_value = raw.into();
+        let value = if let Ok(number) = string_value.parse::<i32>() {
+            CredentialAttributeValue::Number(number)
+        } else {
+            CredentialAttributeValue::String(string_value)
+        };
+
+        self.0 .0.insert(name.into(), value);
     }
 }