Reduce clones and cleanup in block cache path (#6431)

* node: Migrate check_blocks to use typed blocks()

Use the typed `blocks()` method instead of `blocks_as_json()` so that
block comparisons go through the same alloy serialization on both the
cached and provider sides. This gives a fairer diff by normalizing
both blocks through the same types, and only compares the block data
(without receipts) since `eth_getBlockByHash` does not return receipts.

* graph, store: Remove blocks_as_json from ChainStore trait

All callers now use the typed `blocks()` method. The resolver serializes
the CachedBlock to JSON at the GraphQL boundary. This eliminates the
separate raw-JSON code path from the trait.

* graph: Wrap LightEthereumBlock in Arc inside CachedBlock

Arc-wrap the Light variant to avoid expensive deep clones of AnyBlock.
into_light_block now borrows self and returns Arc via cheap refcount bumps.

* graph: Inline EthereumJsonBlock into CachedBlock::from_json

Remove the single-consumer EthereumJsonBlock wrapper and inline its
deserialization and patching logic directly into CachedBlock::from_json.

* graph: Rename to_light_block, add to_json on CachedBlock