feat: Add created_at, updated_at fields in the db proposal model

heromodels/src/models/governance/proposal.rs

@@ -109,6 +109,9 @@ pub struct Proposal {
     pub description: String,
     pub status: ProposalStatus,
 
+    pub created_at: DateTime<Utc>,
+    pub updated_at: DateTime<Utc>,
+
     // Voting event aspects
     pub vote_start_date: DateTime<Utc>,
     pub vote_end_date: DateTime<Utc>,
@@ -134,6 +137,8 @@ impl Proposal {
         creator_name: impl ToString,
         title: impl ToString,
         description: impl ToString,
+        created_at: DateTime<Utc>,
+        updated_at: DateTime<Utc>,
         vote_start_date: DateTime<Utc>,
         vote_end_date: DateTime<Utc>,
     ) -> Self {
@@ -149,6 +154,8 @@ impl Proposal {
             title: title.to_string(),
             description: description.to_string(),
             status: ProposalStatus::Draft,
+            created_at,
+            updated_at,
             vote_start_date,
             vote_end_date,
             vote_status: VoteEventStatus::Open, // Default to open when created