clean up expired reward schedules in fund

This should reduce the computational cost of `calculateLockedShares`
because if we remove expired schedules, which are fully unlocked at that
stage, we need to iterate less elements during the calculation.

src/contracts/aludel/AludelV3Lib.sol

@@ -211,6 +211,8 @@ library AludelV3Lib {
             amount
         );
 
+        cleanupExpiredRewardSchedules(aludel);
+
         // push new reward schedule to the store
         aludel.rewardSchedules.push(
             IAludelV3.RewardSchedule({
@@ -241,4 +243,24 @@ library AludelV3Lib {
         aludel.totalStake += amount;
     }
 
+    function cleanupExpiredRewardSchedules(
+        IAludelV3.AludelData storage aludel
+    ) internal {
+        // check : measure how much gas this actually saves
+        uint256 length = aludel.rewardSchedules.length;
+        for (uint index = 0; index < length; index++) {
+            IAludelV3.RewardSchedule memory schedule = aludel.rewardSchedules[index];
+
+            // check if the period is already expired
+            if (block.timestamp - schedule.start >= schedule.duration) {
+                // length decreces
+                length--;
+                // overwrite current index with last schedule.
+                aludel.rewardSchedules[index] = aludel.rewardSchedules[length];
+                // remove last element, already copied to _index_ 
+                aludel.rewardSchedules.pop();
+            }
+        }
+    }
+
 }