Implement Check Availability Status Functionality

<UserStory> INV004: Check Availability Status </UserStory>

<Changes>
    1. Updated Controller to delegate getInventoryItem calls to InventoryManagementService.
    2. Implemented InventoryManagementService::getInventoryItem to fetch items from datastore by ID.
    3. Enhanced AdminMenu with checkStockAvailability function:
       - Accepts part ID as input.
       - Retrieves item details from Controller.
       - Displays item information (ID, part name, quantity) if found and active.
       - Handles inactive or missing items gracefully.
</Changes>

<Test>

  Precondition:
  1. Admin user is logged into the system.
  2. Inventory contains multiple items with unique IDs.
  3. DataStore is initialized and accessible.

  Steps:
  1. Navigate to Admin Menu and select "Check Stock Availability".
    - Verify that the system prompts for an Item ID.
  2. Enter a valid Item ID for an active item.
    - Verify that the system displays the item’s details including current quantity.
  3. Enter an Item ID that does not exist.
    - Verify that the system displays “Item not found”.
  4. Enter an Item ID for an inactive item.
    - Verify that the system does not display details and indicates the item is inactive.
</Test>

<Review>
Sreeja Reghukumar
</Review>

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/InventoryManagementService.cpp

@@ -1 +1,11 @@
 #include "InventoryManagementService.h"
+
+InventoryItem* InventoryManagementService::getInventoryItem(const std::string& inventoryItemID)
+{
+    int index = m_dataStore.getInventoryItems().find(inventoryItemID);
+    if (index != -1)
+    {
+        return m_dataStore.getInventoryItems().getValueAt(index);
+    }
+    return nullptr;
+}