test(e2e): anchor e2e_amm PXE to checkpointed tip under pipelining (#23336)

## Why

PR #23253 was dequeued (4th attempt) when `merge-queue-heavy` caught an
`e2e_amm.test.ts` setup tx getting dropped by a pipelining-driven chain
prune. CI log: `baec5a7453c20089`.

The wait-for-parent gate in
`CheckpointProposalJob.waitForValidParentCheckpointOnL1`
(`sequencer-client/src/sequencer/checkpoint_proposal_job.ts:398`)
**should** have blocked the discard, but it didn't — because a
`TestDateProvider` time warp from
`AnvilTestWatcher.syncDateProviderToL1IfBehind` landed **between** the
two `epochCache` reads in `Sequencer.work` (`sequencer.ts:217-218`) and
broke the pipelining invariant.

| step | wall-clock | `nowSeconds` | result |
|---|---|---|---|
| 1st `getEpochAndSlotInNextL1Slot` (`slot`) | ≈14:34:32.385 (pre-warp)
| `1778942079` | next L1 ts `1778942080` → **slot 18** |
| (warp at 14:34:32.390 sets offset 7611 → 7610) | | | |
| 2nd `getTargetEpochAndSlotInNextL1Slot` (`targetSlot`) | ≈14:34:32.395
(post-warp) | `1778942080` | next L1 ts `1778942084` → **slot 19** →
`+offset=1` → **targetSlot 20** |

Logged confirmation (gap = 2 instead of 1):

```
14:34:32.612  Preparing checkpoint proposal 19 for target slot 20 during wall-clock slot 18
              {nowSeconds=1778942079, slot=18, targetSlot=20, …}
```

With `slotNow = 18`, the gate at `checkpoint_proposal_job.ts:402` waits
on `waitForSyncedL2SlotNumber(slotNow)`. The archiver had already synced
past slot 18 — the wait returns immediately, far too early to see parent
ckpt 18 (which lands four seconds later at 14:34:36). The gate then sees
`checkpointedNumber=17, parentCheckpointNumber=18`, declares the parent
absent, and discards. Slot 20 expires uncheckpointed, archiver prunes
blocks 19/20, the inflight setup tx anchored to block 19 dies with
`Block header not found`.

Full timeline + log evidence:
https://gist.github.com/AztecBot/4863d10084dd20587bffcc43fd61dfee

## What

Scoped, test-only — per direction from Santiago. The previous "make
`checkpointed` the global PXE default" approach is reverted; only
`e2e_amm` is opted in:

```diff
-    } = await setup(4, { ...PIPELINING_SETUP_OPTS }));
+    } = await setup(4, { ...PIPELINING_SETUP_OPTS }, { syncChainTip: 'checkpointed' }));
```

The PXE option exists already (`yarn-project/pxe/src/config/index.ts`,
added in `75df5b5d44`). This is the same approach every other
pipelining-aware test uses (`e2e_p2p/*`, `e2e_epochs/*`,
`e2e_slashing/attested_invalid_proposal`). It anchors inflight txs to
the L1-confirmed tip so prunes on the proposed tip can't invalidate
them.

`PIPELINING_SETUP_OPTS` is left untouched — the pipelining migration of
`e2e_amm` in #23275 stays.

## Recommended follow-up (separate PR)

The real bug is the race in `Sequencer.work`. Worth fixing properly:

- **Snapshot the time once.** Add
`EpochCache.getCurrentAndTargetSlotInNextL1Slot()` that returns `{slot,
targetSlot, epoch, targetEpoch, ts, nowSeconds}` from a single
`dateProvider.nowInSeconds()` read; replace the two-call site in
`Sequencer.work`. Pipelining offset is a constant, so deriving
`targetSlot = slot + offset` from the same snapshot is trivial.
- **Defensive: wait on `targetSlot - 1`.**
`waitForValidParentCheckpointOnL1` should key off the parent's expected
build slot (`targetSlot - 1`) instead of `slotNow`, so the gate is
robust even if the invariant is broken upstream.

These aren't in this PR because they touch sequencer production code and
want their own review; the test-side workaround unblocks the merge-train
without changing the global PXE default.

## Test plan

The failure requires `merge-queue-heavy`'s 10-grind L1 contention to
surface reliably (single dev box can't reproduce). Change is a
single-arg addition; TS-trivial.

Analysis:
https://gist.github.com/AztecBot/4863d10084dd20587bffcc43fd61dfee

ClaudeBox log: https://claudebox.work/s/166e664eab264b04?run=3

Author: AztecBot

yarn-project/end-to-end/src/e2e_amm.test.ts

@@ -41,12 +41,17 @@ describe('AMM', () => {
   const INITIAL_TOKEN_BALANCE = 1_000_000_000n;
 
   beforeAll(async () => {
+    // Anchor the PXE to the checkpointed tip rather than the proposed tip. Under pipelining the
+    // proposed tip can be pruned when a slot ends without a checkpoint landing on L1 (e.g. when a
+    // time warp races `Sequencer.work`'s two epoch-cache reads and the wait-for-parent gate ends up
+    // pointing at the wrong slot). The checkpointed tip is L1-confirmed and cannot be pruned, so
+    // inflight setup txs survive the race.
     ({
       teardown,
       wallet,
       accounts: [adminAddress, liquidityProviderAddress, otherLiquidityProviderAddress, swapperAddress],
       logger,
-    } = await setup(4, { ...PIPELINING_SETUP_OPTS }));
+    } = await setup(4, { ...PIPELINING_SETUP_OPTS }, { syncChainTip: 'checkpointed' }));
 
     ({ contract: token0 } = await deployToken(wallet, adminAddress, 0n, logger));
     ({ contract: token1 } = await deployToken(wallet, adminAddress, 0n, logger));