Refine the implementation of NumericGroup and Numeric (#102)

## What is the goal of this PR?

We have refined the protocol for returning `Numeric` and `NumericGroup` which are used by match aggregate and match group aggregate respectively.

## What are the changes implemented in this PR?

1. Enrich the representation of `Numeric` such that it can represent long, double, or NaN (not a number)
2. Fix the fact that `NumericGroup` has a list of `Number` rather than `Number`

Author: Ganeshwara Hananda

protobuf/answer.proto

@@ -34,12 +34,15 @@ message ConceptMapGroup {
     repeated ConceptMap concept_maps = 2;
 }
 
-message Number {
-    string value = 1;
-    // We use a string to contain the full representation of a number
+message Numeric {
+    oneof value {
+        int64 long_value = 1;
+        double double_value = 2;
+        bool nan = 3;
+    }
 }
 
-message NumberGroup {
+message NumericGroup {
     Concept owner = 1;
-    repeated Number numbers = 2;
+    Numeric number = 2;
 }

protobuf/query.proto

@@ -69,7 +69,7 @@ message Query {
         }
 
         message Res {
-            Number answer = 1;
+            Numeric answer = 1;
         }
     }
 
@@ -89,7 +89,7 @@ message Query {
         }
 
         message Res {
-            repeated NumberGroup answers = 1;
+            repeated NumericGroup answers = 1;
         }
     }