feat: Multidownloader / L1InfoTreeSyncer: avoid using blockHash = 0x000..0000

[joanestebanr]

If a range have no events on last block the multidownloader create a empty block with hash = 0x00..0000 if the blockNumber is < finalized.

cdk-20260216-212314-aggkit-001  | 2026-06-09T09:23:05.668Z      DEBUG   sync/evmdownloader.go:233       Multidownloader_EVMDownloader.addLastBlockIfNotIncluded: to response From: 237, To: 336 (100) adding empty block number 336 / 0x0000000000000000000000000000000000000000000000000000000000000000 {"pid": 1, "version": "v0.10.0-rc1-18-g76e2488d", "syncer": "l1infotreesync"}