refactor(archiver)!: simplify L2BlockSource block lookups

[spalladino]

⚠️ This PR includes #22870. Reviewers should review only the first commit. ⚠️

Motivation

Consolidates the block-related lookup surface on L2BlockSource from ~17 narrow methods returning ~9 different shapes down to 4 methods returning 2 shapes (L2Block and BlockData). Replaces the per-shape getters with discriminated query objects that carry both the lookup discriminant and a single onlyCheckpointed filter, removing the parallel Checkpointed* API and the throwaway wrapper types.

Additionally, this refactor centralizes block-zero handling in the archiver and threads the dynamic initial header through every component that previously hard-coded the constant, eliminating the divergence and removing the special-case branches in callers.

Approach

L2BlockSource exposes 4 methods that take query objects:

getBlock(query: BlockQuery): Promise<L2Block | undefined>
getBlocks(query: BlocksQuery): Promise<L2Block[]>
getBlockData(query: BlockQuery): Promise<BlockData | undefined>
getBlocksData(query: BlocksQuery): Promise<BlockData[]>

type BlockQuery  = ({number} | {hash} | {archive}) & { onlyCheckpointed?: boolean }
type BlocksQuery = ({from, limit} | {epoch})       & { onlyCheckpointed?: boolean }

On-disk format is unchanged — the archiver already stored block metadata, tx bodies, and per-checkpoint L1/attestation data in separate LMDB maps; CheckpointedL2Block was only an in-memory join produced at read time.

Includes changes from #22870

API surface change

Methods removed from L2BlockSource

getL2Block, getL2BlockByHash, getL2BlockByArchive, getCheckpointedBlock, getCheckpointedBlockByHash, getCheckpointedBlockByArchive, getCheckpointedBlocks, getCheckpointedBlocksForEpoch, getCheckpointedBlockHeadersForEpoch, getBlock(number), getBlocks(from, limit), getBlockData(number), getBlockDataByArchive, getBlockDataWithCheckpointContext, getBlockHeader, getBlockHeaderByHash, getBlockHeaderByArchive.

Types deleted

CheckpointedL2Block, BlockDataWithCheckpointContext — both removed entirely (file + schema + re-exports). Callers that previously read .l1 / .attestations off these now do getBlockData(...) followed by getCheckpointData(blockData.checkpointNumber) and read those fields off CheckpointData.

Types added

BlockQuery, BlocksQuery (and matching Zod schemas) on L2BlockSource. No new domain types — L2Block, BlockData, BlockHeader are unchanged.

AztecNode public RPC

Method names preserved (getBlock, getBlockHeader, getCheckpointedBlocks, etc. — bodies delegate internally to the new L2BlockSource methods). One wire-level change: AztecNode.getCheckpointedBlocks element type goes CheckpointedL2Block[] → BlockResponse[], forced by the type deletion. Older RPC clients that parse the old shape will need to update.

Changes

• stdlib: BlockQuery / BlocksQuery types + Zod schemas next to L2BlockSource. CheckpointedL2Block file deleted; BlockDataWithCheckpointContext removed from block_data.ts. ArchiverApiSchema and MockArchiver shrunk; new it() blocks cover each query discriminant. L2BlockStream migrated.
• archiver: BlockStore consolidates to four query-object reads plus iterators. data_source_base.ts adds resolveBlocksQuery that translates { epoch } → { from, limit } (returns null for empty epochs so callers short-circuit to []). Mocks honor onlyCheckpointed.
• aztec-node: server.ts keeps the public RPC method names but delegates to the new query methods. getCheckpointedBlocks adds a per-call Map<CheckpointNumber, CheckpointData> cache to avoid an N+1.
• consumer migrations: world-state, txe, p2p block-txs handler, validator-client (validator.ts, proposal_handler.ts), pxe block-stream source (honors onlyCheckpointed via node.getL2Tips), prover-node, sequencer-client, telemetry-client, aztec/testing, L2BlockStream in stdlib.
• tests: per-package mocks updated for the new shapes; new test covers getBlocks({ epoch }) empty-epoch returning [].