feat: Add reminder functionality to ContractSigner model

- Added `last_reminder_mail_sent_at` field to track reminder
  timestamps.
- Implemented `can_send_reminder` to check if a reminder can be
  sent based on a 30-minute cooldown.
- Added `reminder_cooldown_remaining` to get remaining cooldown
  time.
- Added `mark_reminder_sent` to update reminder timestamp.
- Added example demonstrating reminder functionality in
  `legal_contract_example.rs`.
- Added tests for reminder functionality in
  `test_reminder_functionality.rs`.
- Updated Rhai scripts to include reminder-related functions and
  tests.
- Improved formatting and clarity in example code.

heromodels/examples/legal_contract_example.rs

@@ -70,7 +70,7 @@ fn main() {
         .add_signer(signer2.clone())
         .add_revision(revision1.clone())
         .add_revision(revision2.clone());
-    
+
     // The `#[model]` derive handles `created_at` and `updated_at` in `base_data`.
     // `base_data.touch()` might be called internally by setters or needs explicit call if fields are set directly.
     // For builder pattern, the final state of `base_data.updated_at` reflects the time of the last builder call if `touch()` is implicit.
@@ -87,7 +87,7 @@ fn main() {
 
     println!("\n--- Contract Details After Signing ---");
     println!("{:#?}", contract);
-    
+
     println!("\n--- Accessing Specific Fields ---");
     println!("Contract Title: {}", contract.title);
     println!("Contract Status: {:?}", contract.status);
@@ -97,7 +97,10 @@ fn main() {
     println!("Updated At (timestamp): {}", contract.base_data.modified_at); // From BaseModelData
 
     if let Some(first_signer_details) = contract.signers.first() {
-        println!("\nFirst Signer: {} ({})", first_signer_details.name, first_signer_details.email);
+        println!(
+            "\nFirst Signer: {} ({})",
+            first_signer_details.name, first_signer_details.email
+        );
         println!("  Status: {:?}", first_signer_details.status);
         if let Some(signed_time) = first_signer_details.signed_at {
             println!("  Signed At: {}", signed_time);
@@ -110,6 +113,51 @@ fn main() {
         println!("  Created By: {}", latest_rev.created_by);
         println!("  Revision Created At: {}", latest_rev.created_at);
     }
-    
+
+    // Demonstrate reminder functionality
+    println!("\n--- Reminder Functionality Demo ---");
+    let current_time = current_timestamp_secs();
+
+    // Check if we can send reminders to signers
+    for (i, signer) in contract.signers.iter().enumerate() {
+        println!("\nSigner {}: {} ({})", i + 1, signer.name, signer.email);
+        println!("  Status: {:?}", signer.status);
+
+        if signer.last_reminder_mail_sent_at.is_none() {
+            println!("  Last reminder: Never sent");
+        } else {
+            println!(
+                "  Last reminder: {}",
+                signer.last_reminder_mail_sent_at.unwrap()
+            );
+        }
+
+        let can_send = signer.can_send_reminder(current_time);
+        println!("  Can send reminder now: {}", can_send);
+
+        if let Some(remaining) = signer.reminder_cooldown_remaining(current_time) {
+            println!("  Cooldown remaining: {} seconds", remaining);
+        } else {
+            println!("  No cooldown active");
+        }
+    }
+
+    // Simulate sending a reminder to the first signer
+    if let Some(first_signer) = contract.signers.get_mut(0) {
+        if first_signer.can_send_reminder(current_time) {
+            println!("\nSimulating reminder sent to: {}", first_signer.name);
+            first_signer.mark_reminder_sent(current_time);
+            println!(
+                "  Reminder timestamp updated to: {}",
+                first_signer.last_reminder_mail_sent_at.unwrap()
+            );
+
+            // Check cooldown after sending
+            if let Some(remaining) = first_signer.reminder_cooldown_remaining(current_time) {
+                println!("  New cooldown: {} seconds (30 minutes)", remaining);
+            }
+        }
+    }
+
     println!("\nLegal Contract Model demonstration complete.");
 }