fix: set anvilSlotsInAnEpoch in e2e_offchain_payment to prevent finalization race (#21452)

## Summary
- Sets `anvilSlotsInAnEpoch: 32` in `e2e_offchain_payment` test setup,
matching what `epochs_l1_reorgs` already does.

## Problem
PR #21156 added `--slots-in-an-epoch 1` as the default for anvil, making
`finalized = latest - 2`. PR #20893 added `e2e_offchain_payment` which
simulates L1 reorgs. When both landed on `merge-train/fairies`, the
reorg test fails deterministically because finalization races past the
rollback target block.

## Fix
Use `anvilSlotsInAnEpoch: 32` (matching Ethereum mainnet) so the
finalized block stays far enough behind latest to allow rollbacks in the
test.

ClaudeBox log: https://claudebox.work/s/c5ac5d52da86e23a?run=4

Author: AztecBot

yarn-project/end-to-end/src/e2e_offchain_payment.test.ts

@@ -29,7 +29,9 @@ describe('e2e_offchain_payment', () => {
   jest.setTimeout(TIMEOUT);
 
   beforeAll(async () => {
-    ({ teardown, wallet, accounts, aztecNode, aztecNodeAdmin, cheatCodes } = await setup(2));
+    ({ teardown, wallet, accounts, aztecNode, aztecNodeAdmin, cheatCodes } = await setup(2, {
+      anvilSlotsInAnEpoch: 32,
+    }));
   });
 
   afterAll(() => teardown());