fix(e2e): use checkpointed chain tip for PXE in epochs and p2p tests

[spalladino]

Summary

Fixes flaky test failures in e2e_p2p and e2e_epochs tests caused by transactions being lost when blocks are pruned due to failed checkpoint proposals.

Problem

The CI test e2e_p2p_valid_epoch_pruned_slash (and potentially other epochs/p2p tests) was failing with a timeout error:

TimeoutError: Timeout awaiting isMined
  at retryUntil (../../foundation/dest/retry/index.js:90:19)
  at DeploySentTx.waitForReceipt (../../aztec.js/dest/contract/sent_tx.js:78:16)

Root Cause

The failure sequence was:

1. Block 2 was built at slot 16 with a deployment transaction
2. Checkpoint proposal failed L1 validation with HeaderLib__InvalidSlotNumber(17,16) - by the time the proposal was submitted, L1 had already moved to slot 17
3. Block 2 was pruned when the archiver detected slot 16 wasn't checkpointed:

   WARN: archiver:l1-sync - Pruning blocks after block 1 due to slot 16 not being checkpointed
   

4. The deployment transaction was lost because it was in the pruned block
5. PXE was syncing to the "proposed" chain tip (default behavior), so waitForReceipt kept waiting for a transaction that would never be mined

Solution

Configure PXE to sync to the checkpointed chain tip instead of the proposed one in both test contexts:

• P2PNetworkTest.setup() - used by all e2e_p2p tests
• EpochsTestContext.setup() - used by all e2e_epochs tests

This uses the newly added syncChainTip PXE config option:

{ syncChainTip: 'checkpointed' }

Why This Fixes the Issue

With syncChainTip: 'checkpointed':

• PXE only considers blocks that have been successfully submitted to L1 (checkpointed)
• Blocks that are proposed but not yet checkpointed are not visible to PXE
• When a checkpoint fails and blocks are pruned, PXE already wasn't tracking those blocks
• Transactions sent through PXE will use anchor blocks from the checkpointed chain, which are stable and won't be pruned

This provides a more stable view of the chain for tests that involve block pruning scenarios.

Changes

• end-to-end/src/e2e_p2p/p2p_network.ts: Pass { syncChainTip: 'checkpointed' } to setup()
• end-to-end/src/e2e_epochs/epochs_test.ts: Pass { syncChainTip: 'checkpointed' } to setup()

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