feat(token_base): add directional rounding support to transfer function

- Add rounding_up: bool parameter to token_base::transfer
- Update a_token_factory::transfer_on_liquidation to use rounding parameter
- Update pool_token_logic::transfer to pass rounding_up=false for user transfers
- Update liquidation calls to use appropriate rounding:
  - Collateral transfer: rounding_up=true (favor protocol, consistent with burn)
  - Protocol fee transfer: rounding_up=false (conservative charging)
- Align with existing mint_scaled/burn_scaled API patterns
- Ensure complete liquidation without dust accumulation

Author: matchv

aave-core/sources/aave-pool/pool_token_logic.move

@@ -156,7 +156,8 @@ module aave_pool::pool_token_logic {
             recipient,
             amount,
             index,
-            a_token_address
+            a_token_address,
+            false // Use round half up for user-to-user transfers
         );
 
         finalize_transfer(

aave-core/sources/aave-tokens/a_token_factory.move

@@ -640,7 +640,14 @@ module aave_pool::a_token_factory {
         // Dust amounts are acceptable to skip as they are too small to be meaningful
         if (amount_scaled == 0) { return };
 
-        token_base::transfer(from, to, amount, index, metadata_address);
+        token_base::transfer(
+            from,
+            to,
+            amount,
+            index,
+            metadata_address,
+            rounding_up
+        );
 
         // Emit event with the actual transferred scaled amount
         // This ensures event accurately reflects the on-chain state change

aave-core/sources/aave-tokens/token_base.move

@@ -506,19 +506,26 @@ module aave_pool::token_base {
     /// @param amount The amount being transferred
     /// @param index The next liquidity index of the reserve
     /// @param metadata_address The address of the token
+    /// @param rounding_up If true, rounds up the scaled amount; if false, rounds half up
     public(friend) fun transfer(
         sender: address,
         recipient: address,
         amount: u256,
         index: u256,
-        metadata_address: address
+        metadata_address: address,
+        rounding_up: bool
     ) acquires ManagedFungibleAsset, TokenBaseState {
         if (amount == 0) {
             return;
         };
         // NOTE: in `ray_div`, while `amount` can be less precision than Ray
         //       precision, `index` must be expressed in Ray precision.
-        let amount_scaled = wad_ray_math::ray_div(amount, index);
+        let amount_scaled =
+            if (rounding_up) {
+                wad_ray_math::ray_div_up(amount, index)
+            } else {
+                wad_ray_math::ray_div(amount, index)
+            };
         assert!(amount_scaled != 0, error_config::get_einvalid_transfer_amount());
 
         // update sender balance