feat: handled internal error properly

[kobayurii]

Previously trait impl<E> From<JsonRpcError<E>> for RpcError was handling only JsonRpcServerError::HandlerError therefore when proxy call returned JsonRpcServerError::InternalError it was sending a "Failed to serialize JsonRpcError" string without any actual details

closes #343

[kobayurii]

@race-of-sloths please, include my PR in the Race

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Reviewer	Score
@khorolets	5

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[khorolets]

@race-of-sloths score 5