* beacon-chain:rpc/eth/shared: prevent mutiple error messages
This commit prevents the error writing function from writing multiple
JSON objects. An error message with more than one JSON object will not
unmarshal into the default error response.
* beacon-chain/rpc/eth/beacon: add a test case for missing state
This commit adds a test on beacon states finality checkpoints endpoint
to cover a case when state is not found.
* beacon-chain/rpc/eth: update error response to meet the spec
This commit updates error message on beacon states finality
checkpoints endpoint to ensure that the response complies to
Ethereum Beacon-API specification.
* beacon-chain/rpc/eth/shared: add build dependency
* beacon-chain/rpc/eth/shared: update test on state not found
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Co-authored-by: Radosław Kapka <rkapka@wp.pl>
