Refactor SsvcDecisionPoint base class mixins (#743)

* create a `_Valued` mixin

* add `_Valued` mixin to base decision point class. Also reorder mixins to adjust default json output key order

* update json examples to reflect new base class mixin ordering

* add len() to _Valued mixin

* add tests

Author: ahouseholder

data/json/decision_points/automatable_2_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Automatable",
+  "description": "Can an attacker reliably automate creating exploitation events for this vulnerability?",
   "namespace": "ssvc",
   "version": "2.0.0",
   "schemaVersion": "1-0-1",
   "key": "A",
-  "name": "Automatable",
-  "description": "Can an attacker reliably automate creating exploitation events for this vulnerability?",
   "values": [
     {
       "key": "N",

data/json/decision_points/cvss/access_complexity_1_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Access Complexity",
+  "description": "This metric measures the complexity of the attack required to exploit the vulnerability once an attacker has gained access to the target system.",
   "namespace": "cvss",
   "version": "1.0.0",
   "schemaVersion": "1-0-1",
   "key": "AC",
-  "name": "Access Complexity",
-  "description": "This metric measures the complexity of the attack required to exploit the vulnerability once an attacker has gained access to the target system.",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/access_complexity_2_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Access Complexity",
+  "description": "This metric measures the complexity of the attack required to exploit the vulnerability once an attacker has gained access to the target system.",
   "namespace": "cvss",
   "version": "2.0.0",
   "schemaVersion": "1-0-1",
   "key": "AC",
-  "name": "Access Complexity",
-  "description": "This metric measures the complexity of the attack required to exploit the vulnerability once an attacker has gained access to the target system.",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/access_vector_1_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Access Vector",
+  "description": "This metric measures whether or not the vulnerability is exploitable locally or remotely.",
   "namespace": "cvss",
   "version": "1.0.0",
   "schemaVersion": "1-0-1",
   "key": "AV",
-  "name": "Access Vector",
-  "description": "This metric measures whether or not the vulnerability is exploitable locally or remotely.",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/access_vector_2_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Access Vector",
+  "description": "This metric reflects the context by which vulnerability exploitation is possible.",
   "namespace": "cvss",
   "version": "2.0.0",
   "schemaVersion": "1-0-1",
   "key": "AV",
-  "name": "Access Vector",
-  "description": "This metric reflects the context by which vulnerability exploitation is possible.",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/attack_complexity_3_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Attack Complexity",
+  "description": "This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.",
   "namespace": "cvss",
   "version": "3.0.0",
   "schemaVersion": "1-0-1",
   "key": "AC",
-  "name": "Attack Complexity",
-  "description": "This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability.",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/attack_complexity_3_0_1.json

@@ -1,10 +1,10 @@
 {
+  "name": "Attack Complexity",
+  "description": "This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. ",
   "namespace": "cvss",
   "version": "3.0.1",
   "schemaVersion": "1-0-1",
   "key": "AC",
-  "name": "Attack Complexity",
-  "description": "This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. ",
   "values": [
     {
       "key": "L",

data/json/decision_points/cvss/attack_requirements_1_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Attack Requirements",
+  "description": "This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack.",
   "namespace": "cvss",
   "version": "1.0.0",
   "schemaVersion": "1-0-1",
   "key": "AT",
-  "name": "Attack Requirements",
-  "description": "This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack.",
   "values": [
     {
       "key": "N",

data/json/decision_points/cvss/attack_vector_3_0_0.json

@@ -1,10 +1,10 @@
 {
+  "name": "Attack Vector",
+  "description": "This metric reflects the context by which vulnerability exploitation is possible. ",
   "namespace": "cvss",
   "version": "3.0.0",
   "schemaVersion": "1-0-1",
   "key": "AV",
-  "name": "Attack Vector",
-  "description": "This metric reflects the context by which vulnerability exploitation is possible. ",
   "values": [
     {
       "key": "P",

data/json/decision_points/cvss/attack_vector_3_0_1.json

@@ -1,10 +1,10 @@
 {
+  "name": "Attack Vector",
+  "description": "This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.",
   "namespace": "cvss",
   "version": "3.0.1",
   "schemaVersion": "1-0-1",
   "key": "AV",
-  "name": "Attack Vector",
-  "description": "This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.",
   "values": [
     {
       "key": "P",