perf: scan allTransactionsList once in the split-save flow

The expense-report transaction filter ran twice per press over the whole
transaction collection - once for areAllExpenseReportTransactionsSplitChildren
and again just to take .length for the last-transaction check.

Hoist it to a single scan. The two consumers disagree on how a missing
expenseReportID should behave, so the guard moves onto the derived value to
keep both behaviours byte-identical rather than onto the scan.

Author: Abdukhamid000

src/libs/actions/IOU/SplitTransactionUpdate.ts

@@ -1956,7 +1956,9 @@ function updateSplitTransactions({
             waypoints: splits.at(0)?.waypoints ? JSON.stringify(splits.at(0)?.waypoints) : undefined,
             copiedComments: splits.at(0)?.copiedComments ? JSON.stringify(splits.at(0)?.copiedComments) : undefined,
         } as RevertSplitTransactionParams;
-        write = () => apiWrite(WRITE_COMMANDS.REVERT_SPLIT_TRANSACTION, parameters, onyxData);
+        write = () => {
+            apiWrite(WRITE_COMMANDS.REVERT_SPLIT_TRANSACTION, parameters, onyxData);
+        };
     } else {
         // Prepare splitApiParams for the Transaction_Split API call which requires a specific format for the splits
         // The format is: splits[0][amount], splits[0][category], splits[0][tag] etc.
@@ -1973,7 +1975,9 @@ function updateSplitTransactions({
         };
 
         const command = isCreationOfSplits ? WRITE_COMMANDS.SPLIT_TRANSACTION : WRITE_COMMANDS.UPDATE_SPLIT_TRANSACTION;
-        write = () => apiWrite(command, splitParameters, onyxData);
+        write = () => {
+            apiWrite(command, splitParameters, onyxData);
+        };
     }
 
     // API.write() applies optimisticData synchronously, so the destination screen re-renders from the
@@ -2019,18 +2023,20 @@ function updateSplitTransactionsFromSplitExpensesFlow(params: UpdateSplitTransac
     // splits belonging to the current expense report, or the only remaining split moved to selfDM.
     // In any of these cases we must navigate away from the soon-to-be-empty report so the user
     // isn't stranded on a "Not Found" page.
-    const expenseReportTransactions = expenseReportID ? Object.values(params.allTransactionsList ?? {}).filter((itemTransaction) => itemTransaction?.reportID === expenseReportID) : [];
+    // Scanned once and reused below. The two consumers differ in how they treat a missing
+    // expenseReportID: areAllExpenseReportTransactionsSplitChildren must see an empty list, while the
+    // last-transaction check historically matched transactions whose reportID is also undefined, so
+    // the guard stays on the derived value rather than on the scan itself.
+    const transactionsMatchingExpenseReportID = Object.values(params.allTransactionsList ?? {}).filter((itemTransaction) => itemTransaction?.reportID === expenseReportID);
+    const expenseReportTransactions = expenseReportID ? transactionsMatchingExpenseReportID : [];
     const areAllExpenseReportTransactionsSplitChildren =
         expenseReportTransactions.length > 0 && expenseReportTransactions.every((itemTransaction) => itemTransaction?.comment?.originalTransactionID === originalTransactionID);
     const anyRemainingSplitStaysInExpenseReport = splitExpenses.some((expense) => expense.reportID === expenseReportID);
     const reverseSplitKeepsOriginalInExpenseReport = isReverseSplitOperation && splitExpenses.at(0)?.reportID === expenseReportID;
     const willExpenseReportBecomeEmpty =
         !!expenseReportID && areAllExpenseReportTransactionsSplitChildren && !anyRemainingSplitStaysInExpenseReport && !reverseSplitKeepsOriginalInExpenseReport;
     const isLastTransactionInReport =
-        willExpenseReportBecomeEmpty ||
-        (isReverseSplitOperation &&
-            !reverseSplitKeepsOriginalInExpenseReport &&
-            Object.values(params.allTransactionsList ?? {}).filter((itemTransaction) => itemTransaction?.reportID === expenseReportID).length === 1);
+        willExpenseReportBecomeEmpty || (isReverseSplitOperation && !reverseSplitKeepsOriginalInExpenseReport && transactionsMatchingExpenseReportID.length === 1);
     const fallbackReportID = params.expenseReport?.chatReportID ?? params.expenseReport?.parentReportID;
 
     if (isLastTransactionInReport && fallbackReportID) {