fix(txe): return FEE_ORACLE_LAG entries from TXEFeeProvider

Addresses PR #22116 review comment 10: mock was returning a single-entry
array instead of matching the production prediction window size.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: spalladino

yarn-project/txe/src/state_machine/global_variable_builder.ts

@@ -1,24 +1,29 @@
 import { BlockNumber, type SlotNumber } from '@aztec/foundation/branded-types';
+import { times } from '@aztec/foundation/collection';
 import type { EthAddress } from '@aztec/foundation/eth-address';
 import type { AztecAddress } from '@aztec/stdlib/aztec-address';
-import { GasFees } from '@aztec/stdlib/gas';
+import { FEE_ORACLE_LAG, GasFees } from '@aztec/stdlib/gas';
 import { makeGlobalVariables } from '@aztec/stdlib/testing';
 import {
   type BuildCheckpointGlobalVariablesOpts,
   type CheckpointGlobalVariables,
+  type FeeProvider,
   type GlobalVariableBuilder,
   GlobalVariables,
 } from '@aztec/stdlib/tx';
 
-export class TXEGlobalVariablesBuilder implements GlobalVariableBuilder {
+/** Simple FeeProvider for TXE that returns zero fees. */
+export class TXEFeeProvider implements FeeProvider {
   public getCurrentMinFees(): Promise<GasFees> {
     return Promise.resolve(new GasFees(0, 0));
   }
 
   public getPredictedMinFees(): Promise<GasFees[]> {
-    return Promise.resolve([new GasFees(0, 0)]);
+    return Promise.resolve(times(FEE_ORACLE_LAG, () => new GasFees(0, 0)));
   }
+}
 
+export class TXEGlobalVariablesBuilder implements GlobalVariableBuilder {
   public buildGlobalVariables(
     _blockNumber: BlockNumber,
     _coinbase: EthAddress,