fix: handle missing L1 finalized block on devnets

[spalladino]

Motivation

On freshly-started L1 devnets (anvil, local geth/reth/nethermind) there is a startup window during which the finalized block tag is not yet available — calls like getBlock({ blockTag: 'finalized' }) fail with a JSON-RPC error instead of returning a block. The archiver currently logs noisy warnings during this window and epoch-cache would crash dereferencing the missing block's timestamp.

Approach

Added a shared getFinalizedL1Block helper in @aztec/ethereum/queries that returns undefined when the chain has no finalized block yet, distinguishing that specific failure from other RPC errors by walking the viem error chain for the "finalized|safe block not found" message (the code -32000 surfaced by geth/reth/nethermind). All three production call sites now handle undefined gracefully: the archiver skips the finalized checkpoint update, and epoch-cache treats entries as "not finalized yet" so they continue to refresh on TTL until the L1 chain catches up.

Changes

• ethereum: New getFinalizedL1Block helper and isFinalizedBlockTagNotFoundError predicate in queries.ts.
• archiver: updateFinalizedCheckpoint uses the helper and returns early with a trace log instead of warning; removed the old "returned no data" substring workaround.
• epoch-cache: refreshStaleEntry and fetchAndCache use the helper and guard the samplingTs <= finalizedBlock.timestamp comparison so entries stay unfinalized when L1 has none yet.
• tests: Unit tests for the helper/predicate, an archiver sync test using FakeL1State configured with no finalized block, and an epoch-cache test asserting entries stay unfinalized and keep refreshing.