fix(taiko-client): reduce slot required for updating lookahead

[cyberhorsey]

we missed 34 slots on Holesky today due to our beacon node having an issue, this means that after current epoch + 2, we need to wait 13 slots to update lookahead. This reduces it to 2 to immediately resolve this issue.

May 23 20:13:05.455 WARN Error when importing rpc blobs          slot: 4344033, block_hash: 0xd4b0be87d0fd60df5dbab17c4ee7e91e2550984ab5a1370b1861896893d55e3c, error: ParentUnknown { parent_root: 0xfc83f9f2c08433772f8ac9f727ca469e6412522003b204ed0bc610b29da12686 }
May 23 20:13:06.000 INFO Syncing                                 est_time: 0 mins, speed: 0.69 slots/sec, distance: 34 slots (6 mins), peers: 102, service: slot_notifier
May 23 20:13:14.362 INFO New RPC block received                  hash: 0xd913747454a718c8cd3e114824bbaa38abe3eab499a91a1208469c26e1383d

beacon missed 34 slots.

Now we make two changes:

1. update lookahead at slot 2 or greater, to minimize the risk of this edge case
2. we only push into the split window slot range ring is we are actually the operator there.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 49 lines in your changes missing coverage. Please review.

Project coverage is 26.50%. Comparing base (b599ffe) to head (20b3652).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/taiko-client/driver/driver.go	0.00%	49 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
packages/taiko-client/driver/driver.go	15.29% <0.00%> (-1.08%)	⬇️

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[Copilot]

Pull Request Overview

This PR fixes an issue with lookahead updates by reducing the minimum required slot from 15 to 2 and adjusting operator conditions when pushing into the window.

• Lowered lookahead update threshold to slot 2
• Refined operator checks and logging paths for current and next operators

Comments suppressed due to low confidence (1)

packages/taiko-client/driver/driver.go:457

• The comment still references using mid-epoch (slot 16) as a reliable point, but the condition now uses slot 2. Please update the comment to reflect the new threshold.

// once per epoch, since we push the next operator as the current range when we check.